Capacitive Position Sensing

ABSTRACT

One or more of the following methods and approaches can be used in capacitive position sensing. For starters, a wireless segmented capacitive sensor that incorporates the capacitive fringing feature; capacitive measurements correlated to position through a map that accounts for fringing. Furthermore, the addition of choice to capacitive sensing, where a sensor can select between two or more groupings to optimize data collection, perform irregularity detection, identification, avoidance and or adaptation. As well, the method of specialized pads. Another method involves the creation and application of intentional irregularities embedded into the scale. Such irregularities serve to encode higher order information into the scale, such as but not limited to absolute position information. Finally, intentional changes to the slider and or scale pads, particularly to oversize and or shape pads for the purpose of tolerating misalignment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of provisional patent application Ser. No. 62/674,989, filed May 22, 2018 by the present inventors.

BACKGROUND OF THE INVENTION

Without a doubt, measurement is important, and by extension, measurement devices. However, measurement devices are also important for another reason. Control systems use sensors extensively. A control system, in accordance to its namesake, uses available historical and current data to make decisions. The better the sensor data, the better the performance.

Capacitive sensing techniques are very popular because they tend to use relatively simple parts and components. For instance, many capacitive encoders are just specially designed pads on a printed circuit board, or PCB. Since PCB's can be mass produced with high accuracy and low cost, capacitive sensors are a desirable sensing method.

Capacitive Sensing

Many different capacitive position sensing techniques are outlined in FIG. 1, General Concepts Overview Map. The figure attempts to show a block diagram of underlying concepts and ideas, as well as to provide examples of these concepts in prior art patents. This is part of a description of the known information and the state of existing technology. Please note that dashed boxes illustrate relevant patents. Solidly outlined boxes highlight concepts. Lines between solid boxes indicate that the ideas connect or give way to one another. An idea will typically give way to another from top to bottom. For instance, linear sensors give way to linear interpolation and connect to wired interpolation approaches.

The general topics outlined in FIG. 1 need to be reviewed to lay the groundwork of the state of technology. To do that efficiently, the prior art has been summarized according to topic:

1. Linear Sensors (A0) 2. Threshold Counting (B0) 3. Interpolation (C0) 4. Wired Capacitive Sensor Basics (D0) 5. Wireless Capacitive Sensor Basics (E0) 6. Phase Modulation (F0) 7. Same Signal Phase Modulation (G0) 8. Orthogonal Signal Phase Modulation (H0) 9. Differential (I0) 10. Shield Electrode and Signal Balanced Shield Electrodes (J0) 11. Multiple Electrodes (K0) 12. Absolute Positioning (L0) 13. Phase Construction (M0)

There are also six papers that explore topics highly relevant to fringe effects in capacitive sensing. These will be discussed later in the Most Relevant Prior Art section. An exhaustive list of prior art can be found listed in the references cited section.

State of Technology

To understand where capacitive sensing can be taken, it is important to see where capacitive sensing has come from. For this reason, it is useful to briefly review the state of technology.

1. Linear Sensors (A0)

Linear sensing refers to the core assumptions that different sensors use. Linear capacitive position sensors refer to the capacitance being driven by the parallel plate effect. The capacitance is directly and linearly proportionate to the overlapping area between two (or more) electrodes that form the capacitor.

Historically most capacitive sensors approximate linear sensing by ignoring effects like fringing and parasitic capacitance. All sensors experience some degree of fringing. However, provided the exposed area is high, the edges are few and the gap between capacitor pads is relatively small, then the fringing of the electric field lines is low or negligible.

2. Threshold Counting (B0)

Some sensors count discrete capacitive highs and lows. Each high or low represents one increment or threshold. Sensors can use these discrete increments to determine or help determine position.

3. Interpolation (C0)

Interpolation refers to estimating or evaluating position between maxima or minima thresholds.

4. Wired Capacitive Sensor Basics (D0)

Capacitive sensors typically have emitter(s) and receiver(s). In a wired sensor, either the emitter is placed on the scale and the receiver on the slider, or vice versa.

5. Wireless Capacitive Sensor Basics (E0)

The inherit limitations of wired sensors was overcome by way of capacitive coupling. Capacitive coupling implies that separate conductive pads(s) are placed between emitter and receiver pad(s). The signal pathway between pads is: emitter—separate conductive pads—receiver. Often times, separate conductive pads are part of a scale. The emitter and receiver pads are typically part of the slider. As the scale moves relative to the slider, the capacitive coupling changes.

6. Phase Modulation (F0)

Phase modulation is a common capacitive sensing approach used in various encoders. Multiple signals are emitted at different positions. These signals may be of the same type but different phase. This can be called Same Signal Phase Modulation (G0). These signals may also be of different type. This can be called Orthogonal Signal Phase Modulation (H0).

As the slider moves, it lines up differently with the scale. This occurs periodically along the length of the scale. The receiver(s) will sense a waveform that is a combination or superposition of these emitted signals. Depending on where the sensor is, that combination will vary. For instance, there may be three emitted signals, A, B and C. Sometimes the received signal will be more like A, B, C or somewhere in-between any two signals. How much the received signal is like A, or B or C defines the signal phase. The signal phase can be compared to a reference phase to determine position. A situation with three emitted phases and one received signal is modeled here:

Signal0=A1(x)·Signal1+A2(x)·Signal2+A3(x)·Signal3

In this equation, Signal1, Signal2 and Signal3 are emitted signals. Signal0 is a received signal based on the capacitive coupling of each emitted signal with the receiver. As the sensor moves, the capacitive coupling changes. As the capacitive coupling changes, the contribution of each emitted signal to the received signal changes. This change is reflected in components A1(x), A2(x) and A3(x). Each signal's respective contribution to or amplitude in Signal0 is modeled by these A(x) position dependent coefficients. Traditionally, these coefficients have been to assumed to follow a linear (parallel plate) relationship.

7. Same Signal Phase Modulation (G0)

Same signal phase modulation implies that each emitted signal is of the same shape. That shape may be square, sinusoidal, saw-tooth or some other distinct shape. The phase refers to the emitted signals varying in time delay. Usually each emitted signal is somewhere from 0 to 360 degrees out of phase relative to the other signal(s). For example: a sensor may have phases A, B and C. Phase A may be at 0 degrees of phase. Phase B may be at 120 degrees of phase. Phase C may be at 240 degrees of phase. In this example, the receiver will see a single waveform that is some superposition of the emitted signals. This single waveform will vary anywhere from 0 to 360 degrees in phase. Of course, the pattern repeats every 360 degrees. The sensor will evaluate the position based directly on comparing the received signal phase to a reference phase.

8. Orthogonal Signal Phase Modulation (H0)

Orthogonal signal phase modulation implies that each emitted signal is of different shape or type. Signals are orthogonal to one another in time and or frequency. The receiver sees some superposition of the emitted signals. The sensor will evaluate position based directly on decomposing the received signal into its constituent parts. The relative intensity of each constituent signal defines the phase.

For example:

Consider two emitted signals, A and B. Sometimes the received signal would be entirely A, entirely B or some superimposed combination. The relative superposition or ratio of one signal to another is effectively a phase.

The phase can be evaluated because the emitted signals are orthogonal. The received signal can be disentangled into its constitute parts. From this, relative intensity and phase can be determined, and position evaluated.

It is also important to note that a sensor based on emitted signals of different frequency is essentially a Frequency Modulation sensor.

9. Differential (I0)

Differential is similar to the concept of twisted pair common mode rejection. The emitted signals are often split into pairs. For instance, signal A may become A+ and A−. The A+ and A− signals are spaced close together, so that any noise impacts both similarly or effectively the same.

Differential is typically done by doubling the number of emitted signals. Each emitted signal will have a positive and negative half. The number of unique receivers is also doubled, into pairs. Typically, each received signal pair subtracts the received positive and negative signals from one another:

(A+)−(A−)=2A

This subtraction eliminates or reduces common mode noise. This boosts Signal to Noise Ratio (SNR) of the device.

10. Shield Electrode and Signal Balanced Shield Electrodes (J0)

Shield electrode sensors have emitter(s) and receiver(s). A cover or shield is between these elements. This cover blocks or changes the capacitive coupling by what is covered and uncovered.

Differential techniques give way to signal balanced shield electrodes. The assumption here is that the shield electrode is floating independent of a DC ground. Clever geometry design choices allow all emitter pads to be equally exposed to the shield at all times. Thus the shield is balanced to all emitted signals. The shield, being exposed to balanced emitted signals should always have a constant DC value potential. In this way, it can block electric field lines without a physical ground, neutral or DC connection. The shield acts to cover and uncover the emitter pads in a specific way as it moves along. Phase—modulation techniques can be used with the added benefit of this covering shield. Outside noise may interfere with the shield's balance. The shield itself may need to be shielded from outside interference

11. Multiple Electrodes (K0)

Many capacitive sensors have more than one receiver electrode. Electrodes may be in successive groups. These groups may be evenly spaced in some periodic or non-periodic manner Having multiple electrodes serves several useful purposes:

-   I. Multiple electrodes can be used to check for faults or errors, as     seen in US patents like U.S. Pat. No. 4,743,902. Two (or more)     electrode groupings are often placed side by side. A measurement is     taken from each grouping and compared. If the two measurements are     in agreement, then the measurement is valid. If the measurements do     not agree, then there is a problem. -   II. Some position measurement techniques use the difference between     any two measurements to obtain position information, like in U.S.     Pat. No. 8,854,054 B2. -   III. Use of multiple electrodes can enable the input signal to be of     differential type. Examples of this can be seen in U.S. Pat. Nos.     4,420,754, 4,743,838, 5,304,937, US 2005/0092108 A1 and U.S. Pat.     No. 6,892,590 B1. -   IV. Multiple pads in parallel can increase the Signal to Noise Ratio     (SNR) by increasing capacitive coupling, like in the cited paper “A     Simple Capacitive Displacement Sensor”, published in the 1991     journal of Sensors and Actuators by F. Zhu and J. W. Spronck and can     be seen in many US patents, like U.S. Pat. Nos. 4,743,902,     4,788,546, 4,841,225, 4,879,508, 5,977,781, US 2005/0092108 A1 and     U.S. Pat. No. 6,892,590 B1. -   V. Random defects can be a source of error. The impact of these     defects can be averaged out by having periodic electrode pads     connected in parallel. This is discussed in papers like “A Simple     Capacitive Displacement Sensor,” published in the 1991 journal of     Sensors and Actuators by F. Zhu and J. W. Spronck, as well as some     US patents, like in U.S. Pat. No. 4,743,838. -   VI. Systematic defects can be sources of error. The impact of these     defects can be reduced by having electrodes spaced in non-periodic     patterns. This is discussed in more detail in the U.S. Pat. No.     5,977,781. -   VII. Multiple pads can increase sensor resolution by implementing     the vernier effect. Resolution is theoretically increased by     staggering pads at different intervals, like in U.S. Pat. No.     5,304,937.

12. Absolute Positioning (L0)

Capacitive sensors tend to use principles that lead to relative information. For instance, phase modulation sensors measure relative position in any given period. Each period occurs across some interval of spatial distance. To make this type of sensor more accurate, one generally needs to shorten the size of each interval. The shorter the interval, the greater the total number of intervals along the length. Each interval will be indistinguishable from every other interval. As the number of repeating intervals increase, determining absolute position becomes a problem.

To circumvent this problem, many sensors index against a reference. However, there are many circumstances when the sensor may not be indexed against a reference or may lose that indexing. In these cases, the sensor does not know its absolute position. Recall, a greater number of total intervals will make it less clear which interval the sensor is in.

To summarize:

-   -   To know position absolutely, one needs to be referenced to an         absolute starting position     -   The system will have to continuously monitor its position         relative to this absolute starting position. If, for example,         power is interrupted while the slider is moving, the absolute         starting reference would be lost. After every use, the sensor         will need to be continuously powered, or the slider locked in         place or referenced before each next use.         Some absolute positioning methods allow the sensor to operate         with the same or similar relative exactness, except without the         need to re-reference the sensor.

How has this been achieved?

The author of U.S. Pat. Nos. 4,420,754 and 4,879,508 proposes a simple method. The author proposes the use of two different phase patterns. The scale has two rows (or perhaps more). Each row has a different pad spacing. Since each row has a different spacing, both rows incur phase at different rates. This difference is slight. Sometimes the two signals, one from each row, are similar in phase. Sometimes the two signals are very different in phase. The difference between the rows is a higher order waveform embedded into the scale. This higher order waveform provides absolute position information.

Other authors have proposed similar solutions. For instance, U.S. Pat. No. 6,892,590 B1 proposes embedding a higher order waveform in a circular encoder, using a second row; this encoder is circular instead of linear. One row (or ring) is for relative and the other for absolute position information.

Using multiple rows is a simple way to add additional information to the sensing. This addition, however, requires additional space for the different rows, not to mention the additional electrical hardware required.

Also, authors often use multiple rows for differential filtering. The extra space required for the extra rows for differential and for absolute positioning could cause space limitation pressures.

13. Phase Construction (M0)

Phase construction involves receiving one net waveform through multiple measurements. A single signal is emitted. Many different receiving electrodes or electrode sets are used to measure the capacitive distribution. The one net waveform is constructed by the superposition of these many measurements. The phase or position of this net waveform determines the sensor position measurement.

SUMMARY

Concepts (1.) to (13.) are common building block concepts that can and have been used in the creation of existing encoders.

Most Relevant Prior Art

A focus of the invention is around how capacitive fringe principles can be applied and incorporated. There are several existing prior art examples where authors discuss capacitive sensing, in the context of fringing as it pertains to the invention. It is important to review these documents. First and foremost, to establish existing prior art. Secondly, to evaluate shortcomings and limitations. Thirdly, for the purpose of distinguishing new from prior art.

Relevant Prior art and Shortcomings:

“A Simple Capacitive Displacement Sensor”, published in the 1991 journal of Sensors and Actuators by F. Zhu and J. W. Spronck—the authors of this paper propose a wired, phase construction type, capacitive sensor. In this paper, the authors create a sensor with micrometer sized plates. By taking eight, side by side measurements, the authors reconstruct an overall pseudo-sinusoidal waveform. By taking many subsequent measurements, the author bypasses dealing with the fringing. Provided the electric field distribution or waveform shape varies in some discernible way, then the waveform phase can be detected. The phase corresponds to relative position.

This sensor has several drawbacks. The sensor exists in a laboratory setup only. It requires eight separate measurements from eight separate receiver pad sets. Each measurement must be taken at the same time, or close together in time. This is necessary to create a reasonable snapshot. To maintain a high Signal-To-Noise ratio, each of the eight sets must have many pads in parallel. This increases the sensor size. The sensor is also wired, making it impractical.

“A New Linear Encoder-Like Capacitive Displacement Sensor”, published in the 2006 Measurement journal, V39, by Moojin Kim, Wonkyu Moon, pp 481-489, and “A New Capacitive Displacement Sensor with High Accuracy and Long-Range”, published in the 2006 Sensors and Actuators A journal, 130-131, by Moojin Kim et al, pp 135-141—both papers discuss the same or similar wired, nano-coated, amplitude based capacitive sensor. Capacitance is measured using an impedance analyzer. The capacitance is then correlated with a position. The authors discuss a fundamental aspect of capacitive sensing: fringing, linearity and sensitivity is dependent on the gap between the scale and the slider. In order to maximize the sensor performance, the author's propose minimizing the gap distance. To achieve a thin gap, a hyperthin diamond like coating was used. The slider and scale are both coated, then pressed against one another. In doing this, the sensor performance is maximized

The author's discussion shows one way to improve sensor performance. However doing so is not always possible or practical, especially outside of the laboratory.

The proposed sensor requires special fabrication, particularly for the hyper thin coating. It is also wired. To be practical, the sensor should be wireless. Wireless sensors eliminate the need to physically tether the scale and the slider together. This makes the sensor more durable and resistant to noise.

The tether (often a loose wire) may be of similar length to the scale itself. Often encoders operate in busy environments with other nearby equipment or moving machinery. A wire could get caught or snagged, damaging its connection with the sensor or perhaps dislodging from the sensor itself. A wire catching can also create a workplace safety concern. Regardless of the specific tethering mechanism, a physical connection is subject to wear and degradation overtime.

The tether or physical connection can also be susceptible to electromagnetic interference, receiving noise like an antenna and reducing the signal to noise ratio (SNR) and potentially reducing sensor accuracy. Wireless sensing helps to circumvent these issues, while often reducing the number of components in a sensor.

Wireless sensing is more practical for real world applications.

“A Time-Grating Sensor for Displacement Measurement with Long Range and Nanometer Accuracy”, published in the 2015 IEEE Transactions on Instrumentation and Measurement journal by Ziran Chen et al, pp 3105-3115—this paper proposes a wired, micrometer sized differential phase modulation capacitive sensor. The author's base assumption is linear (parallel plate), that capacitance is linearly related to area overlap, and that the position linearly correlates with capacitance. The authors note that sensor pad and gap dimension ratios have a large impact on sensor performance, particularly gap size and pad spacing. These results agree similarly with the results found in “A New Linear Encoder-Like Capacitive Displacement Sensor”, published in the 2006 Measurement journal, V39, by Moojin Kim, Wonkyu Moon, pp 481-489, and “A New Capacitive Displacement Sensor with High Accuracy and Long-Range”, published in the 2006 Sensors and Actuators A journal, 130-131, by Moojin Kim et al, pp 135-141. The authors note fringing as a source of error.

The authors' base mathematical assumptions are to ignore fringe. This inevitably leads to errors and deficient sensor performance. To make the sensor a bit better, the authors rely on a SiO2 coating between the top and bottom pads. This requirement adds additional complexity with only a slight improvement on performance. The sensor is also wired, making it impractical for real world applications.

“A Novel Single-Excitation Capacitive Angular Position Sensor Design”, published in the 2016 Sensors (Basel) journal by Bo Hou et al—this paper proposes a differential, phase modulation radial encoder. The sensor also appears wireless in nature. The author's base assumption is linear (parallel plate). The authors note a repeating, pseudo-sinusoidal error. By measuring the non-linearity, the authors create a correction equation. This correction equation increases the positioning accuracy from about 0.25 degrees to about 0.008 degrees.

The authors discuss sources of error. These sources assume flaws in the realization of their design. The four suggested flaws are:

1. Manufacturing and installation error 2. Differences between theoretical and actual capacitance, related to electrode shape 3. Stray capacitance (noise from cables, etc) 4. Pads soldered on the stator (presumably causing surface irregularities)

Points 1, 3 and 4 are possible. However, point 2 is the most relevant. Point 2 states that the theoretical and actual capacitive coefficients differ; that the actual capacitance, at different positions, differs from the calculated capacitance. According to their data, this is true. The theoretical model predicts a different position than the actual position, resulting in error. However, this is not an actual reason for the discrepancy. This is merely restating that there is a discrepancy.

Why might this discrepancy exist? In the paper, the error pattern repeats six times. The error is pseudo-sinusoidal in nature. Likewise, there are six iterations of electrode patterns. From the perspective of the invention proposed in this patent, it is intuitively clear that some if not most of the error is a result of fringe effects.

The authors attempt to address the error with a correction stage. In doing this, they illuminate what is true for many, if not all, capacitive position sensors: these sensors will benefit by accounting for fringing effects in their capacitive models. In this case, the authors improve the sensor performance by several orders of magnitude, though not by intent of harnessing fringing but rather by default of observing error.

The authors propose reducing error by changing the electrode shape. How changing the electrode shape will reduce error is not discussed. Ultimately, all sensors experience some degree of fringing. Changing the shape of the electrodes will not change this fact. This is unavoidable. Instead, one should embrace fringing, applying and using it as effectively as possible. This is preferable over ignoring it and then coming up with additional, after the fact correction steps and stages.

In short, if the apriori capacitive model was more accurate, then the fringing would not have been an error. It would have been an expectation.

“Efficient Design of Capacitive Sensors Using Conformal Maps”, published in the 2012 IEEE International Instrumentation and Measurement Technology Conference Proceedings journal by Graz, N. Eidenberger, S. Wiesmueller and B. G. Zagar, pp. 1308-1313.—in this paper, the authors propose a methodology for aiding in the design of capacitive sensors. This is done by improving the ease and speed of calculating electric field distributions. The authors propose a way of applying the conformal mapping Schwarz-Christoffel Transform (SCT). A warping technique is also used to optimize the approximations by adjusting the blade position. The results are compared against industry accepted numerical simulation approach, Finite Element simulation Method (FEM). The proposed model appears to have a high degree of accuracy against the numerical simulation.

Calculating electric field distributions with conformal mapping is faster than simulation methods, such as FEM. However, this paper does not talk about sensors or sensing itself. The authors do not discuss what kind of capacitive sensor this mapping is for. For instance, would someone use this for a capacitive proximity sensor? Would someone use this for a capacitive position encoder? The authors talk about how to map nonlinear electric field distribution, but they do not talk about how to take advantage of it, how to apply it or how to sense with it. For these reasons, this paper is not comparable to the invention proposed in this patent.

In Review, In Context

The next two paragraphs summarize details from the embodiments to help distinguish what is new from what is prior art.

A task of this invention is to optimize the fringing feature or nature present in capacitive position sensors or encoders. This is to be done in such a way that, at most, only one measurement reading is necessary to evaluate relative position information; that specialized lab setups, exotic fabrication techniques or materials are unnecessary; that the sensors are as practical as possible, being ideally wireless in nature; that the fringing is not an error or a problem but rather an expectation.

Moreover, the task of this invention is to optimize fringing, to improve sensor accuracy and performance, and also to enhance, imbue and enable new features, aspects and abilities into capacitive position sensors or encoders.

Description of Known Information, Conformal Mapping and Fringe

The paper, “Efficient Design of Capacitive Sensors Using Conformal Maps” by N. Eidenberger et al in 2012, proposes a specific conformal mapping technique. Their results are highly accurate. However, their technique appears mathematically intense. It seems applicable only to certain geometries. There are other conformal mapping techniques that can be repurposed for use in capacitive position encoders.

In “An Analytical Fringe Capacitance Model for Interconnects Using Conformal Mapping”, published in the V25, No. 12, December 2006 edition of IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, conformal mapping and analyzing capacitance by parts is proposed. In that paper, the authors approximate capacitance of stationary objects, mosfet and transistor structures. In particular, their mapping pertains to flat and rectangular shapes, as visualized in FIG. 2. This approach is of particular interest for capacitive sensor plates. Their technique, used on stationary objects, can be borrowed and repurposed for moving objects, moving objects like capacitive encoder pads.

Conformal mapping applied here acts to warp the electric field distributions from their curvy or curvy-linear shapes into straight shapes in a new spatial plane. In the new plane, parallel plate capacitance models can be applied. The equations that transform from one plane to another can be applied through the parallel plate model to build an overall (nonlinear) capacitance model that accounts for fringing. The method proposed in the paper, “An Analytical Fringe Capacitance Model for Interconnects using Conformal Mapping”, published in the V25, No. 12, December 2006 edition of IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, is summarized in the following points, (1) to (4).

Four mapping techniques

1. Radial Mapping (conformal) 2. Perpendicular Plate Mapping (conformal) 3. Edge Effects (analytical) 4. Offset Parallel Plate Mapping (conformal)

Note: It is important to realize that the field line diagrams, FIG. 2 to FIG. 9, are for the purpose of visualizing electric field shape. They are not accurate with respect to electric field intensity or electric flux density. The electric field intensity is best represented through the particular mapping equations.

1. Radial Mapping—is visualized in FIG. 3. In this figure, components (T), (H) and (W) are dimensional quantities, relevant for the conformal mapping equation. Components (M), (N), (O), and (P) are used to help visualize how the left maps to the right. Radial mapping is a good conformal mapping method to study for the purpose of understanding the other mapping techniques. In short, it is an analogy. The equations resulting from radial mapping can be seen here:

$C = {\left( \frac{2 \cdot ɛ}{\pi} \right) \cdot {\ln \left( {1 + \frac{T^{\prime}}{W}} \right)}}$ $T^{\prime} = {{\left( {e^{{(\frac{1}{\tau})} \cdot {({1 + \frac{T}{W}})}} \cdot T} \right)\mspace{14mu} {where}\mspace{11mu} \tau} \approx 3.7}$

In this instance, a circle is mapped from an X-Y domain to a magnitude-angle domain, U-V. In this new domain, the previous circular geometry is now rectangular. In a sense, the shape goes from a circle in a rectangular coordinate system to a rectangle in a circular coordinate system. Unlike polar or spherical coordinates, which maintain visual accuracy, the new coordinate system is not ‘round’. Rather the new coordinates are circular quantities represented in a Cartesian plane.

2. Perpendicular Plate Mapping (conformal)—is visualized in FIG. 4 and FIG. 5. In FIG. 4, components (T), (H), (S) and (W) are dimensional quantities relevant to the Conformal mapping equations. (CPERP) refers to Cperpendicular or perpendicular capacitance. In FIG. 5, components (T), (H), (S) and (W) are dimensional quantities, same as in FIG. 4. Components (M), (N), (O), and (P) are used to help visualize how the left maps to the right. Note: perpendicular plate mapping is analogous to radial mapping, as radial mapping is a subset case of perpendicular plate mapping. The equations resulting from this perpendicular plate conformal mapping can be seen here:

$C = {\left( \frac{2 \cdot ɛ}{\pi} \right) \cdot {\ln \left( \frac{H + T^{\prime} + \sqrt{S^{2} + T^{\prime^{2}} + {2 \cdot H \cdot T^{\prime}}}}{S + H} \right)}}$ $T^{\prime} = {{{\left( e^{(\frac{W + S - \sqrt{S^{2} + T^{2} + {2 \cdot H \cdot T}}}{\tau \cdot W})} \right) \cdot T}\mspace{14mu} {where}\mspace{11mu} \tau} \approx 3.7}$

This system represents the electric field lines traveling perpendicular to the main and broad surface of the plates, not the edges. The electric field lines perpendicular to the surface represent the action of the electrons distributed across this surface, but not any extra electrons bunched up at the edges.

The perpendicular field lines can be connected together by a curvy shape, like in FIG. 5. By observation, this shape is elliptical. In radial mapping, the mapped quantities are radius and angle. In this case, the proposed axis quantities are ellipses and hyperbola.

3. Edge Effects (analytical)—are visualized in FIG. 6 and FIG. 7. Edge effects are from the extra electrons bunched up at and near the edges. The edge effects have been broken down into edge effects on a plane (FIG. 6) and edge effects along a diagonal line of displacement (FIG. 7).

CED-I, where CED is shorthand for CEDGE, and CED-I or CEDGE-I indicates edge capacitance along a plane. Components (S) and (T) are dimensional quantities relevant to the capacitive equations described below.

CED-II, where CED is shorthand for CEDGE, and CED-II or CEDGE-II indicates edge capacitance along a diagonal line of displacement. Components (S) and (H) are dimensional quantities relevant to the capacitive equations described below.

Edge effects are not mapped conformally, but can be used in conjunction with conformal mapping to quantify or analyze a system. Edge effect equations were analytically proposed based on governing principles such as electric fields being inversely proportionate to the distance between edges. The proposed equations were evaluated empirically. They are represented by the following:

CED-I—edge effects along a plane:

$C = {\frac{ɛ}{\pi} \cdot e^{\frac{- {({T + S})}}{3 \cdot S}}}$

CED-II—edge effects along a diagonal line of displacement:

$C = {\frac{ɛ}{\pi} \cdot \sqrt{\frac{H \cdot S}{H^{2} + S^{2}}}}$

4. Offset Parallel Plate Mapping (conformal)—Is visualized in FIG. 8 and FIG. 9. In FIG. 8, components (T), (H), (W), (S) and (H′) are dimensional quantities relevant to the capacitance equations below. In FIG. 9, components (M), (N), (O), and (P) are used to help visualize how the left maps to the right.

Offset Parallel plate mapping is an extension to the principles in perpendicular plate mapping. The capacitance is broken down into three parts:

(1) Extension of Perpendicular Plates (CPI)

(2) Edge effects along a Plane (CED-I)

(3) Standard Parallel Plate (CPAR)

By observation, the net capacitance can be described by the equivalent circuit diagram seen in FIG. 8. The capacitive behavior has been summarized in the following equations:

${C = {{\frac{4 \cdot ɛ}{\pi} \cdot {\ln\left( \frac{H + {\eta \cdot T} + \sqrt{S^{2} + \left( {\eta \cdot T} \right)^{2} + {2 \cdot H \cdot \eta \cdot T}}}{S + H} \right)}} + {2\frac{\left( {ɛ \cdot W \cdot \alpha \cdot \left\lbrack {{\ln \left( {1 + \frac{2 \cdot W}{S}} \right)} + e^{- {(\frac{S + T}{3 \cdot S})}}} \right\rbrack} \right)}{\left( {{W \cdot \pi \cdot \alpha} + {\left( {H + T} \right) \cdot \left\lbrack {{\ln \left( {1 + \frac{2 \cdot W}{S}} \right)} + e^{- {(\frac{S + T}{3 \cdot S})}}} \right\rbrack}} \right)}} + {2\frac{ɛ \cdot T \cdot \beta \cdot \left\lbrack {{\ln \left( {1 + \frac{2 \cdot T}{H}} \right)} + e^{- {(\frac{H + W}{3 \cdot H})}}} \right\rbrack}{{T \cdot \pi \cdot \beta} + {\left( {S + W} \right) \cdot \left\lbrack {{\ln \left( {1 + \frac{2 \cdot T}{H}} \right)} + e^{- {(\frac{H + W}{3 \cdot H})}}} \right\rbrack}}} + {\left( \frac{ɛ}{\pi} \right) \cdot \sqrt{\frac{H \cdot S}{H^{2} + S^{2}}}}}}\mspace{14mu}$   where   ɛ = dielectric  Permittivity $\mspace{20mu} {\eta = e^{\frac{W + S - \sqrt{S^{2} + T^{2} + {2 \cdot H} + T}}{\tau \cdot W}}}$ $\mspace{20mu} {\beta = e^{- {(\frac{S + W}{H + T})}}}$ $\mspace{20mu} {\alpha = e^{- {(\frac{H + T}{S + W})}}}$   τ ≈ 3.7

SUMMARY

These four techniques assume that electric field lines do not bend into or out of the page. This is true for certain situations; field lines are generally negligible when the shapes are long and rectangular in nature relative to the cross-section of interest. The capacitance of a sensor can be evaluated using conformal mapping. The sensor electrodes for an encoder will move. At each position, the capacitance can be evaluated. The conformal mapping equations can be tuned with their fitting factors and constants. The level of tuning dictates how closely the calculated capacitance will match the actual capacitance.

Conformal mapping can be used both qualitatively and quantitatively. Conformal mapping is an approach that can be used to quickly analyze capacitive behavior. This is useful for intuitive design work. Conformal maps can also be improved for final design work, enabling high accuracy simulations.

Ultimately, numerical simulation methods are the gold standard for evaluating electromagnetic field distribution. However, numerical methods tend to be slow. Papers like “A New Linear Encoder-Like Capacitive Displacement Sensor”, published in the 2006 Measurement journal, V39, by Moojin Kim, Wonkyu Moon, pp 481-489, explain that analytical solutions and representations are difficult to obtain. With conformal mapping, this work is a lot faster. It is now faster and more practical to work and design with fringe effects. It is also possible to develop closed form approximations based on the conformal mapping data analogous to those found in “Efficient Design of Capacitive Sensors Using Conformal Maps”, published in the 2012 IEEE International Instrumentation and Measurement Technology Conference Proceedings journal by Graz, N. Eidenberger, S. Wiesmueller and B. G. Zagar, pp. 1308-1313.

BRIEF SUMMARY OF THE INVENTION

Capacitive position sensors and encoders need to be precise and accurate. They need to operate predictably and provide repeatable measurements. Authors in prior art have explored a number of topics, methods and approaches to fulfill these goals. Most prior art ignores fringing effects. Some prior art marginalizes fringing. This has been done through careful design choices, size ratios and or with exotic coatings or materials. One prior art bypasses nonlinear fringing complications. This is done by taking many consecutive measurements and constructing an overall waveform.

In short, prior art attempts various methods of circumventing and or avoiding the very real impact of fringing effects.

In this invention, one goal is to embrace and optimize the fringing feature. How can this ever-present fringing behavior be applied, used and optimized to benefit and even simplify sensor operation?

This can be done first and foremost by introducing a simplified single emitter, single receiver approach, like in the circuit in FIG. 11 and the block diagram and pad layout in FIG. 12. The emitter pads are all connected together in parallel. By connecting these electrodes or pads together in parallel, the crosstalk between the emitter pads becomes irrelevant. The receiver pads are all connected together in parallel. By connecting these electrodes or pads together in parallel, the crosstalk between the receiver pads becomes irrelevant.

The scale is segmented, comprised of many conductive pads along its length. The capacitive coupling between the slider and the scale creates a wireless connection. The offset varies the strength of the wireless connection, the magnitude of the capacitive coupling. The capacitive coupling can be analyzed with apriori analysis, deterministic nonlinear analysis and fringing analysis. Through this analysis, the coupling can be represented or modeled in the form of equation(s), transfer function(s), lookup table(s), and or other forms. The position can be interpreted through one or more of these models.

Using only a single receiver which obtains only a single measurement at a time, this approach is simplified over many prior art. The sensor requires less hardware and or less signal processing software. The sensor can also be of smaller size. Peak thresholds can be used to keep track of position intervals. The incremental or relative position interpolation accuracy within an interval is improved over standard linear (parallel plate) assumptions. The present invention is also more practical, incorporating and effectively using wireless capacitive coupling.

In the previous discussion of known information, conformal mapping and fringing analysis techniques make it clear that capacitive position sensors experience fringing. Phase modulation capacitive sensors are one example. Looking at this example, it is clear how fringing models can improve sensor performance in existing sensors, like phase modulation sensors. Sensors such as phase modulation sensors actually operate on a compound amplitude modulation principle. The phase modulation is caused by each phase contributing a portion of amplitude to the resulting net signal. This amplitude contribution is based on a nonlinear fringing relationship, not just a linear relationship. Given the measurement of the resulting output signal, and apriori knowledge of the nonlinear fringe relationship, the position can be discerned more clearly. In this way, the present invention can be incorporated into many existing capacitive sensors to improve positioning accuracy.

The present invention has and enables a multitude of other benefits. Briefly:

-   -   Multiple Groupings—multiple groups provides choice. Choice         enables the opportunity for data collection optimization.         Choice, as specifically outlined in this section also enables         irregularity detection, irregularity recognition, irregularity         avoidance, irregularity adaptation and data selection         optimization. Other benefits also exist.     -   Specialized Pads—apriori capacitive behavior and fringing         knowledge makes it possible to create specialized pads for the         purpose of deriving specialized information. Subsequently,         specialized pads can be used in conjunction with multiple         groupings to develop specialized prescanning. These pads can be         used to provide shielding. They also simplify irregularity         detection, adaptation, avoidance and alerts. Other benefits also         exist     -   Absolute Positioning—unique features will leave or imbue unique         signatures on the capacitive waveform. Apriori capacitive and         fringing knowledge will enable the detection of and discernment         between unique features. This enables concise and streamlined         absolute position sensing or marker detection. Other benefits         are also possible.     -   Embedded Components—feature detection can also be extended for         the detection of unique components embedded into the scale.     -   Oversized pads—oversized pads on the scale and or the slider can         be used to resist certain misalignment errors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1—shows a map of general prior art concepts, connections and examples. (A0) represents the concept of Linear Sensors. (B0) represents the concept of Threshold Counting. (B1) represents patents that embody principle (B0). (C0) represents the concept of Interpolation. (D0) represents the concept of Wired Capacitive Sensor Basics. (D1) represents a patent that embodies principle (D0). (E0) represents the concept of Wireless Capacitive Sensor Basics. (F0) represents the concept of Phase Modulation. (F1) represents patents that embody principle (F0). (G0) represents the concept of Same Signal Phase Modulation. (G1) represents patents that embody principle (G0). (H0) represents the concept of Orthogonal Signal Phase Modulation. (H1) represents patents that embody principle (H0). (I0) represents the concept of Differential. (I1) represents patents that embody principle (I0). (J0) represents the concept of Shield Electrode and Signal Balanced Shield Electrodes. (J1) represents patents that embody principle (J0). (K0) represents the concept of Multiple Electrodes. (K1) represents patents that embody principle (K0). (L0) represents the concept of Absolute Positioning. (L1) represents patents that embody principle (L0). (M0) represents the concept of Phase Construction. (M1) represents patents that embody principle (M0).

FIG. 2—shows a visualization of electric field line paths, from an isometric perspective (left) and end on view (right). A capacitor is formed from surfaces (01) and (02), an anode and cathode respectively. The electric field lines visualize the combination of simple parallel plate and various fringing effects. This figure is not intended to represent actual field line density.

FIG. 3—shows a visualization of the fringing electric field line paths, and in this case of radial, perpendicular plate effects. The figure is an end on conceptualization, before (left) and after (right) conformal mapping. Quantities (T), (H) and (W) are dimensional quantities, relevant to the formulas in the conformal mapping section. Points (M), (N), (O), and (P) are used to help visualize how the left maps to the right. X-Y is the original Cartesian coordinate system, U-V is the new coordinate system after mapping. The figure is an end-on conceptualization, and is not intended to represent actual field line density.

FIG. 4—shows a visualization of the fringing electric field line paths and in this case of perpendicular plate effects (left), with a reminder of the equivalent circuit representation (right). CPERP represents a shorthand for Cperpendicur, referring to the perpendicular plate effects. Quantities (T), (H), (S) and (W) are dimensional quantities, relevant to the formulas in the conformal mapping section. The figure is an end-on conceptualization, and is not intended to represent actual field line density.

FIG. 5—shows a more formal visualization of fringing electric field line paths and in this case from perpendicular plate effects, before (left) and after (right) conformal mapping. Quantities (T), (H), (S) and (W) are dimensional quantities, relevant to the formulas in the conformal mapping section. Points (M), (N), (O), and (P) are used to help visualize how the left maps to the right. X-Y is the original Cartesian coordinate system, U-V is the new coordinate system after mapping. The figure is an end-on conceptualization, and is not intended to represent actual field line density.

FIG. 6—shows an end-on visualization of fringing electric field lines from edge effects along a plane (left) with a reminder of the discrete equivalent circuit representation (right). Quantities (S) and (T) are dimensional quantities, relevant to the formulas in the conformal mapping section. (CED-I) is a shorthand to refer to CEDGE, or edge capacitance along a plane. The figure is not intended to represent actual field line density.

FIG. 7—shows an end-on visualization of fringing electric field lines from edge effects along a diagonal line of displacement (left), with a reminder of the discrete equivalent circuit representation (right). Quantities (S) and (H) are dimensional quantities, relevant to the formulas in the conformal mapping section. (CED-II) is a shorthand to refer to CEDGE, or edge capacitance along a diagonal line of displacement. The figure is not intended to represent actual field line density.

FIG. 8—shows an end-on visualization of fringing electric field lines from the offset parallel plate fringing effects (left) and a reminder of the equivalent circuit representation (right). This fringing effect is the combination of three component effects: 1. Extension of Perpendicular Plates Effects (CPI) 2. Edge effects along a Plane (CED-I), 3. Standard Parallel Plate (CPAR). Quantities (T), (H), (W), (S) and (H′) are dimensional quantities relevant to the formulas in the conformal mapping section. The figure is not intended to represent actual field line density.

FIG. 9—shows a visualization of the fringing electric field line paths from extension of perpendicular plate effects. Points (M), (N), (O), and (P) are used to help visualize how the left maps to the right. X-Y is the original Cartesian coordinate system, U-V is the new coordinate system after mapping. The figure is not intended to represent actual field line density.

FIG. 10—shows a simplified visualization of the proposed sensor, with (10) being a slider, moving along or over-top of a scale, (20). The associated circuitry (microcontroller, digital logic circuits, analog circuits, etc) are not shown for simplicity but would likely be located on or in the slider. The mechanical structure that the slider and scale attach to is not shown for simplicity and should be well understood by someone skilled in the art of capacitive sensing.

FIG. 11—shows one possible circuit representation or embodiment of the sensor described in FIG. 10 and FIG. 12. Component (03) describes any undesirable capacitive effects, like cross capacitance and parasitic capacitance. These undesirable capacitive effects are neglected from future diagrams for simplicity. (11) refers to emitter pad(s). (12) refers to receiver pad(s). (21) is the part of a scale pad or segment that capacitively couples with (11). (22) is the part of a scale pad or segment that conductively connects (21) and (23). (23) is the part of a scale pad or segment that capacitively couples with (12). Component (05) is a Signal Generator that energizes (11). (04) is the load impedance visualized here as a resistor. (VOUT) refers to the received signal being measured.

FIG. 12—shows two things: 1, an operational block diagram of how the electronics interface with the pads (left), and 2, how those pads could be arranged spatially (right and lower). Component (05) is the Signal Generator. Component (06) is the Signal Conditioning Unit. Component (07) is the Demodulation Unit. Component (08) is the Processing Unit for processing Nonlinear Signals. Component (11-1) is an emitter pad that makes up (11). Component (12-1) is a receiver pad that makes up (12).

FIG. 13—shows a simplified overhead visualization of the sensor proposed in FIG. 12.

FIG. 14—shows a visualization of the slider's path of movement along the scale. In this example, the mechanically linear slider can move back and forth in the X-direction.

FIG. 15—shows a visualization of a nonlinear capacitive waveform (30), that would result from the pads moving past one another. (Wd) is a dimensional quantity, referring to the relative displacement between the slider and scale along the X axis.

FIG. 16—shows a visualization of the slider's path of movement around a scale, in a radial case example.

FIG. 17—shows a visualization of how a shielding, component (13), can be distributed around the slider's emitter and receiver pads.

FIG. 18—shows a visualization of how the slider and scale could be notched to improve shielding Component (22-P) is the variation of component (22) that involves the routing of a conductive connection to another side of the scale.

FIG. 19—is a top down view of how multiple groupings could be realized, with offset emitter and receiver groupings. Components (11A) and (12A) form an emitter—receiver grouping. Components (11B) and (12B) form another emitter—receiver grouping.

FIG. 20—is a cross-sectional side view of how multiple groupings could be realized. The horizontal dotted line represents the divide between the physical pad placement and the purely electrical routing of components (11A) through (13). The precise routing path(s) are not specifically relevant to the matter being explored by this figure. The vertical dotted lines show how the slider's groupings align with the scale's segments or pads.

FIG. 21—is an exaggerated diagram to give a sense how fringing effects impact or deviate from the otherwise linear capacitive behavior. Waveform (31) represents an idealized, linear capacitive waveform. Waveform (32) represents a more realistic capacitive waveform when nonlinear fringing capacitive effects are taken into account. It is noteworthy in (32) that the slope changes along an interval.

FIG. 22—is a waveform representation of multiple groupings. Dotted line (33A) represents the waveform associated with one grouping. Dotted line (33B) represents the waveform associated with another grouping. The two groupings are offset from one another by 90 degrees, or V2 the width of a pad. Plot (A), the top plot, represents possible waveforms from both groups. Plot (B), the middle plot, represents the waveforms when the sensor performs a scan and hold, switching at the vertical lines of intercept. Plot (C), the bottom plot, represents a possible waveform from both groups, when the sensor constructs one overall waveform from the two waveforms. (R1) represents the first region, (R2) the second region, (R3) the third region, (R4) the fourth region. The purpose of showing two (R1) regions is to illustrate the fact that the overall waveform is cyclical or repetitive.

FIG. 23—is a top down view of how multiple groupings could be realized, with one large emitter and two offset receiver groupings. (12A) shows one receiver grouping, and (12B) shows another receiver grouping.

FIG. 24—is a simplified equivalent circuit diagram visualization of FIG. 23. (VSELECT) refers to the digital selection of the analog connection or pathway. (04A) represents one load impedance. (04B) represents another load impedance. Each load impedance is associated with a receiver grouping. (09) represents the switching element or circuitry for altering which grouping is connected to the rest of the Signal Conditioning Unit, component (06). In this case, the switching element is a MUX.

FIG. 25—shows a cross-sectional side view representation of the a prescanning sensor with a bit of debris, (50), on the scale. This is shown for the purpose of visualizing how the sensor could detect the debris, (50), in advance, and track it. In this depiction, the debris is in the region of group A. If the slider moves to the left, in the negative X direction, then the debris will end up in the region of group B. The horizontal dotted line represents the divide between the physical pad placement, and the purely electrical routing of components (12A) through (14). The precise routing path is not specifically relevant to the matter being explored by this figure. Component (14) represents specialized pads in the form of prescanning pads.

FIG. 26—shows a possible pad specialization, in particular, prescanning pads. The prescanning pads are represented by (14A), (14B), (14C) and (14D). In theory, either (14A) or (14B), (14C) or (14D) could be emitter or receiver pads, respectively.

FIG. 27—shows another possible pad specialization approach, particular for prescanning pads designed for detecting certain misalignment errors. (14A-1) and (14A-2) are a specialized split form of (14A) prescanning pads. (14B-1) and (14B-2) are a specialized split form of (14B) prescanning pads. (14C-1) and (14C-2) are a specialized split form of (14C) prescanning pads. (14D-1) and (14D-2) are a specialized split form of (14D) prescanning pads.

FIG. 28—shows a visualization of unique pad features, oversized scale pads, described by (21-1A) and (23-1A). This configuration could be used to provide absolute position information. (20-1) represents the center of the unique pad feature. (Ws) represent the spacing of the scale pads, which in this case is uniform.

FIG. 29—shows a visualization of the capacitive waveform generated by the unique pad features described in FIG. 28. The waveform is denoted by waveform (34). (20-1) represents the center of the unique pad feature defined by (21-1A) and (23-1A). In this example, the middle peak in (34) occurs when the center of the unique pad (20-1) is centered with the slider's receiver pads, at a point of complete overlap. (Ws) represents the spacing of the scale pads in FIG. 28, showing up in the capacitive waveform's (34) periodicity

FIG. 30—visualizes some of the many different configurations of components (21), (22) and (23), components of a scale pad. On the left, all three components are on the same plane. In the middle, (22-P1) is on a different plane than (21) and (23). On the right, (22-P2) is on a different plane than (21). (23-P2) may be on the same plane, or different plane as (22-P2), but is certainly on a different plane than (21).

FIG. 31—visualizes the difference between a straight (22) connection and a possible crossed connection depicted by (22-C1) and (22-C2), in a top down view.

FIG. 32—visualizes a double layer sensor with two groupings, grouping A and grouping B. (10A) is slider side A. (11A), is the grouping A emitter. (12A) is the grouping A receiver. (21A), (22A) and (23A) are the components that make up a segment in the scale for side A, the side that couples with group A. (10B) is the slider side B. (11B) is the grouping B emitter. (12B) is the grouping B receiver. (21B), (22B) and (23B) are the components that make up a segment in the scale for side B, the side that couples with group B.

FIG. 33—visualizes a crossover for a double layer sensor with two groupings, grouping A and grouping B. (10A) is slider side A. (11A), is the grouping A emitter. (12A) is the grouping A receiver. (21A) and (23A) are the components that make up a segment in the scale for side A, the side that normally couples with group A. (22A-C) is a crossover connection between layers, from the bottom side (21B) to the top side (23A). (10B) is slider side B. (11B) is the grouping B emitter. (12B) is the grouping B receiver. (21B) and (23B) are the components that make up a segment in the scale for side B, the side that normally couples with group B. (22B-C) is a crossover connection between layers, from the top side (21A) to the bottom side (23B).

FIG. 34—is a visualization of an asymmetric intentional irregularity on the scale, characterized by a trapezoidal pad shape, components (21-1B) and (23-1B).

FIG. 35—shows a visualization of embedded components on the scale vs no embedded components, depicted by the two different cases: (22-P) vs (22-PD). (22-P) represents case where the scale conductive connection goes to the other side of the scale, but does not have an associated discrete or embedded component. (22-PD) represents a case where the scale conductive connection goes to the other side of the scale, and does have a discrete or embedded component. It doesn't necessarily matter where the component is embedded, but on the other side of the scale seems convenient. The embedded or discrete component is visualized as (42). In this case, the left shows a simplified isometric view and the right shows a simplified circuit diagram, where component (42) is an inductor. However component (42) could be any embedded component or components, it does not have to be an inductor.

FIG. 36—is a top down visualization of how pads could be oversized. In this case, the slider pads are longer than the scale pads, denoted by components (11C) and (12C).

FIG. 37—is another top down visualization of how pads could be oversized. In this case, the slider pads represent a BatWing shape, denoted by components (11D) and (12D). This shape is intended to be resistant against rotational and offset misalignment. Other shapes are also possible.

DETAILED DESCRIPTION OF THE INVENTION

Capacitive encoders need to be precise and accurate. Capacitive encoders need to operate predictably and provide repeatable measurements. Authors have explored a number of topics, methods and approaches to fulfill these goals. Many of these sensors have been limited by the availability of technology. Modern approaches have looked at ways of squeezing out every last bit of exactness possible.

Fringing wasn't mentioned in most prior art. However, it seems that a few authors were aware of fringing effects. Some authors ignored fringing in their base assumptions, some made design choices to marginalize it and some bypassed it.

Intentional and meaningful capacitive fringing on a segmented conductive scale is possible for a wireless encoder. A segmented conductive scale is heterogeneous in nature, being composed of separate conductive components with non conductive aspect(s) holding it all together, such as a printed circuit board (PCB). Capacitance can be measured by how an applied high frequency signal is modulated. Of course, any suitable method for measuring the circuit's capacitance could be used instead.

A visualization of an encoder can be seen in FIG. 10. This can be seen as the template model that embodiments build on, with a slider (10) and a segmented scale (20). An equivalent circuit can be seen summarized in FIG. 11. Even with the best shielding, undesirable capacitive effects like parasitic capacitance can still arise, as described by components (03). Parasitic capacitance will be omitted from future circuit diagrams for ease of presentation. It is understood that a reader skilled in the art of capacitive sensing will understand parasitic capacitance.

A simplified circuit and flow diagram have been modeled in FIG. 12. Components (11) and (12), are the emitter and receiver plates, respectively. These parts would be located on the slider, component (10). Components (21), (22) and (23), comprise aspects of one complete scale element or segment, a scale pad. Components (11) and (21) capacitively couple together. Component (22) provides a conductive conduit for a signal to travel from (21) to (23). Components (23) and (12) capacitively couple together. Variable capacitance is represented as capacitors with diagonal arrows through them, as seen in FIG. 11 and FIG. 12.

Constituent circuitry for components (05), (06), (07) and (08) is not shown for simplicity, but like many prior art, it should be well understood that such components would be located on or integrated in the slider.

FIG. 13 shows a top down view of the slider and scale. In the renditions like FIG. 12, the emitter and receiver pads are shown as separate entities. Rectangles, such as (11-1) that make up (11) would be connected together conductively, typically by circuit board traces. Rectangles such as (12-1) that make up (12) would be connected together conductively, typically by circuit board traces. However, other shapes and configuration are possible. For instance, it is possible for either the emitter or receiver pads to be one large pad instead of many parallel, smaller pads. However, it is generally preferable that that at least either the emitter or receiver pads have many narrow segments, to maintain accuracy; having one large pad for the emitter and one large pad for the receiver, in the same design, is generally not desirable.

If the encoder is mechanically linear, then the slider moves back and forth along and above the scale, like visualized in FIG. 14 and FIG. 15. If the encoder is mechanically radial, then the slider rotates around the scale like in FIG. 16. The slider could also move along a radial or curvi-linear scale, if desired.

This basic layout can be modified for phase modulation, amplitude modulation or other configurations.

Most embodiments will likely be constructed out of traditional materials, like printed circuit board (PCB). Other construction techniques are also possible, such as but not limited to lithography. However, the same principles still apply. The construction and fabrication, as well as other mechanical details, are not expected to vary greatly from existing prior art. Rather, what will vary is the base assumptions and principles used as well as how they are applied and manifested. The circuitry may deviate. Most fabrication details will be considered well known by someone already skilled in the art. For example, shielding techniques, be it active or passive, should already be well known by someone knowledgeable in the field of capacitive sensing. However, some embodiments do require specialized or unique considerations. The new or specialized nature of these instances will be discussed case by case.

In this patent, there are many embodiments. These embodiments cover a wide range of applications and implementation of various capacitive sensing concepts, with a special focus on fringing. For ease of review, they are summarized here:

EMBODIMENT 1: (Simple AM)

EMBODIMENT 2: (Enhancing Prior Art)

EMBODIMENT 3: (Multiple Groupings)

EMBODIMENT 4: (Pad specialization)

EMBODIMENT 5: (Absolute Positioning)

EMBODIMENT 6: (Embedded Components)

EMBODIMENT 7: (Oversized Pads)

The embodiments and their concepts can be combined in any reasonable combination of one or more.

Embodiment 1 Simple AM

All capacitive sensors experience some degree of fringing. Most sensors marginalize the fringing, often at the penalty of needing exotic solutions or having reduced performance. Some sensors bypass fringing, by taking many side-by-side measurements and constructing an image. The location of the image is the position. Some authors observe error, the deviation from linear expectations, and then add an additional correction stage. Had their capacitive model been more accurate, then deviations would not have been an error, it would have been an expectation.

The sensor developed here is intended to operate with the fringing that is, and not the linearity that one wishes. It is necessary to discuss the foundation such a sensor could be built on. It is important to keep in mind where fringing concepts need to be considered in the sensor foundations. In particular:

A. the design of the slider—scale pads, where the capacitive behavior occurs

B. the model relating measurements to position, where capacitive behavior is interpreted.

Amplitude modulation is a good foundational basis for this sensor. It clearly reveals the role of fringing in the capacitance to position relationship. The principles in amplitude modulation can be generalized for other sensor types, like phase or frequency modulation capacitive sensors.

The sensor discussed in this embodiment can be outlined as having the following components, consistent with FIG. 11 and FIG. 12:

1. Signal Generator Unit 2. Capacitive Circuitry Unit 3. Signal Conditioning Unit 4. Demodulation Unit 5. Processing Unit 1. Signal Generator Unit

The Signal Generator, component (05), operates by energizing (11) with a high frequency signal. It is connected to the emitter pads as seen in FIG. 11 and FIG. 12. This signal could be any alternating, or pulsing signal, but would generally and conveniently be a square wave between 10 KHz-1 GHz; a square wave can be easily generated by a pulse width modulator (PWM) component, found in many microcontrollers. Other signal generating methods or components are also possible.

2. Capacitive Circuitry Unit

The capacitive circuitry in this sensor can be seen as components (11) to (21), (22) and (23) to (12), as illustrated in FIG. 11 and FIG. 12.

Components (11) and (12) comprise the slider as emitter and receiver, respectively. Components (21), (22) and (23) are what comprise a segment on the segmented scale. In this sensor, operation is simple. The slider moves along the scale. The overlap between the slider and scale pads change as the position of the slider changes. The amount of overlap changes the amplitude of the capacitance.

The nature of the scale pads is important. Many of the Most Relevant Prior Art rely on a wired connection between the slider and the scale. To make the sensor practical outside of the laboratory, the sensor must be wireless. Wireless coupling is enabled by having components (21), (22) and (23). This way, the signal emitted from (11) travels to (21) by the capacitive coupling between them. The signal travels from (21) through the conductive channel (22) to (23). At (23), the signal can travel back to the slider by capacitive coupling between (23) and (12).

The emitter pads can all be connected electrically parallel. Hence, only a single signal generator is needed. The receiver pads can all be connected electrically in parallel. Hence, only a single signal receiver circuit is needed. Since the emitters and receivers are all in parallel, then the circuit is simplified in comparison to the paper “A Simple Capacitive Displacement Sensor”, published in the 1991 journal of Sensors and Actuators by F. Zhu and J. W. Spronck or U.S. Pat. No. 4,743,838. Instead of sensing many different pads and ‘constructing’ a capacitive distribution or image, it need only to sense all pads together. Only a single measurement is obtained at a time. Only a single measurement needs to be processed at a time, instead of many side by side measurements. This leads to a more compact and simplified design. Moreover, when many pads are in parallel, the cross-talk between the pads connected in parallel is not relevant.

The receiver-emitter layout can be shielded. One example of shielding can be seen in FIG. 17. Component (13) represents a possible shield electrode placement. The level of shielding is based on manufacturing techniques available and the desired complexity of the sensor. The shielding can be passive, or active. More advanced shielding arrangements are also possible, like the indented shielding seen in FIG. 18. Component (13) provides shielding in this case. It is also possible to implement differential techniques, like those discussed in State of Technology.

These slider and scale pad elements need to function in such a way as to vary the amplitude of the capacitance as the slider moves along the scale. In order to do that, the pads are spaced apart so that overlap can change. This can be seen in how the slider pads line up with the scale pads in FIG. 12 and in FIG. 15, where pads are shown to slide past one another.

In theory, the emitter could be one solid pad, or many individual pads in parallel. Typically, the greater the number of individual pads, the more fringing that will occur. It is important to design the sensor pads with fringing in mind. To balance fringing with parallel plate capacitance, the number of individual emitter pads could be optimized. The size of each pad, as well as their spacing can also be optimized. If half as many pads are chosen, then each pad may be twice as large. A similar principle is also possible with the receiver pads.

The width of each slider pad should also be balanced against the gap distance along the Y-axis between the slider and the scale. The greater the gap, the more fringing that occurs.

3. Signal Conditioning Unit

The received signal should be preprocessed using a Signal Conditioning Unit, component (06), as seen in FIG. 12. This unit may perform any number of tasks. Tasks may include one or more of the following: impedance matching stage(s), variable load impedance stage(s), high impedance input amplifier stage(s), differential common mode noise rejection stage(s), center frequency tunable band pass filter stage(s) and noise rejection stage(s). Not all of the components listed above have to be used, nor do they have to be in the order listed above. The order listed above gives a feel for how these components could be arranged, one feeding the next, feeding the next, and so on. Adjustable components, like the variable load or tunable filter, can be set with outputs from the Processing Unit (08). Other methods of tuning and or setting these adjustable components are also possible.

Note: A high impedance input amplifier is ideal for buffering the input signal with negligible impact on the effective impedance or overall input impedance seen by the signal at (12) when looking into the receiving circuitry. The receiving circuitry can be seen as the Signal Conditioning Unit and the Demodulation Unit. Many low cost, off the shelf micro-controllers come with built-in differential and high impedance amplifiers. One example is Cypress's PSOC 4 series chips.

The implementation of a differential stage should be well understood by someone skilled in the art of electronics and capacitive position sensors. The operation and implementation of filter stage(s) should be obvious to someone already skilled in the art of electronics. Impedance matching is well known in the field of transmission theory.

A load impedance can be used to reduce signal reflections and improve the signal to noise ratio. This is done by impedance matching. However, it may be desirable to have an adjustable load impedance for other purposes.

To make the load impedance adjustable, the magnitude and or electrical characteristics should be adjustable. This can be achieve by constructing the variable load out of discrete parts, like resistors, inductors and capacitors. These components can be in parallel and or series configurations. By adjusting the connection and configuration of the discrete parts with the appropriate switching circuitry, the load impedance becomes adjustable. Other components can be used instead, like a discrete, digitally controlled variable resistor.

Regardless of how the load impedance is made variable, the key element here is that it is adjustable.

What use is variable load impedance?

A variable load impedance is part of the receiving circuitry. Varying the load impedance can change input impedance of the receiving circuitry. Changing the input impedance of the receiving circuitry can change the amplitude of the received signal. This change can be modeled according to the following equation:

${Vout} = {{Vin} \cdot \left( \frac{Zload}{{Zload} + {Zcapacitor}} \right)}$

-   -   where Vout is the received signal     -   where Vin is the emitted signal     -   where Zload is the receiving circuitry input impedance, being         comprised by the variable load impedance and the impedance of         the rest of the receiving circuitry     -   where Zcapacitor is the impedance of the capacitive circuitry         defined by (11) to (12).

The receiving circuitry will have a finite range of operation. Within this range of operation will exist a range of optimal function. If Vout has a potential amplitude range wider than the range that can be normally or optimally supported by the receiving circuitry, then it is useful to use the load impedance to adjust the amplitude accordingly.

Given an adjustment to the variable load impedance, how will Zcapacitor be calculated?

It is a simple matter to determine the capacitive impedance (Zcapacitor) despite adjustments in the variable load impedance, as described in the following equation:

${Zcapacitor} = {\left( {\frac{Vout}{Vin} + 1} \right) \cdot {Zload}}$

-   -   where Vout is measured     -   where Vin is known     -   where Zload is set by adjusting the variable load impedance     -   where Zcapacitor is calculated.         -   Calculations such as these can be preformed in the             Processing Unit.

4. Demodulation Unit

The preprocessed signal should be fed into a Demodulation Unit, component (07) as seen in FIG. 12, to extract the envelope. This may be achieved through any reasonable method such as but not limited to demodulation circuitry, analog and or digital (hardware), and or digital demodulation signal processing (software).

This stage should contain the analog to digital conversion system, likely an ADC. If the demodulation occurs in hardware, the ADC should come after the demodulation circuitry.

5. Processing Unit

The demodulated signal, the envelope, does not linearly correlate to displacement. The relationship is certainly nonlinear, as visualized by waveform (30) in FIG. 15. (Wd) is a dimensional quantity, referring to the relative displacement of the slider along the X axis relative to the scale. The envelope or received signal intensity correlates to the circuit impedance. Knowing the intensity of the emitted signal and the intensity of the received signal, relative displacement within an interval can be calculated through nonlinear capacitance model(s) that account for fringing. The models can be implemented with equations, transfer function(s), lookup tables or other methods. These calculations are done in the Processing Unit, component (08). The Processing Unit is likely a microcontroller, but could be implemented using any other reasonable processing circuitry or system.

The Processing Unit can also be used to control or set any features in the Signal Conditioning Unit that are adjustable as necessary or desired.

The number of peaks and valleys, or whole intervals traversed can be tracked by the Processing Unit (08) to compile an accurate view of the overall displacement.

To increase performance, a history of one or more past or recent measurements can be retained in memory. This way, the next or current measurement can be compared against a series of one or more previous measurements. This also allows the decoding of speed and acceleration from displacement. Speed can be evaluated or approximated by taking the derivative between different displacement measurements. Acceleration is likewise the second order derivative. Consistency can be evaluated using a number of metrics. For instance, the acceleration or velocity data can be used ensure points of discontinuity are caught. The next or current reading can also be compared to previous readings to determine consistency. If the measurements are inconsistent, IE one does not follow the others within some boundary of expectation, then by virtue the sensor has detected atypical situations such as but not limited to, fault conditions.

There are many ways of determining consistency. For instance, the next position measurement should be reasonably consistent with previous position measurements, speed and acceleration measurement(s) or approximations. For instance, using the last known position, the time interval between samples, and the velocity, it is possible to estimate the next position. If the next position measurement and the estimated position measurement do not agree closely, then a fault has likely occurred. The next measurement should also follow along the capacitive waveform. If it does not, then that is another fault situation.

Generalizing to Other Capacitive Sensing Techniques

The previously outlined concepts form the basis for an amplitude modulation capacitive sensor. The five outlined units can be generalized to three modules:

1. Capacitive Circuitry Module

-   -   Capacitive Circuitry Unit

2. Measurement Module

-   -   Signal Generator Unit     -   Signal Conditioning Unit     -   Demodulation Unit

3. Interpreting Module

-   -   Processing Unit

where the function of these modules can be generalized as follows:

1. Capacitive Circuitry Module: this module creates the capacitive property being measured. For most sensors, this amounts to either a variation in capacitive amplitude or capacitive coupling. 2. Measurement Module: this module is what interacts with and extracts measurements from the capacitive circuitry being measured. 3. Interpreting Module: this module is what makes sense of the collected data, correlating the measurements with the respective position information.

These functions are the basic aspects, tasks or operations in every capacitive position sensor, regardless of type.

Fringe modeling, considerations and concerns apply regardless of the capacitive sensor type. In amplitude modulation sensors, the amplitude is a nonlinear waveform due to fringing. In other sensors such as phase and frequency modulation sensors, the coupling between each of the emitted signals, the scale, and the receiver varies nonlinearly due to fringing. The change in coupling changes the ratio of how much of each emitted signal is received. This coupling can be described by the capacitance of each individual component. The capacitance between each emitted signal and the scale varies according to a nonlinear fringe relationship. The capacitance between the scale and the receiver varies according to a nonlinear fringe relationship. The coupling from the emitters, through the scale and to the receiver is nonlinear according to the individual elements that experience fringing. Hence, the overall phase varies nonlinearly with position.

The pad layout, sensor design and interpreting module should take fringing into account. Regardless of the capacitive sensor type, all sensors benefit from recognizing and incorporating the effects of fringing in both the mechanical design and modeling calculations.

Embodiment 2 Enhancing Prior Art

This embodiment serves to support the generalized discussion in the first embodiment. Many commonly used wireless capacitive sensors with segmented scales, like phase modulation sensors, have one or more emitted and or received signals. Directly or indirectly, these sensors rely on the capacitance between the slider and scale.

As seen in, “A Time-Grating Sensor for Displacement Measurement with Long Range and Nanometer Accuracy”, published in the 2015 IEEE Transactions on Instrumentation and Measurement journal by Ziran Chen et al, pp 3105-3115 and “A Novel Single-Excitation Capacitive Angular Position Sensor Design”, published in the 2016 Sensors (Basel) journal by Bo Hou et al, it is common, industry standard to assume a linear relationship between the measurement and the position. However, this assumption is in error and the nonlinearities cannot be adequately ignored. Capacitive and deterministic effects like fringing, cross-talk and parasitic effects change an ideality of linearity into the reality of non-linearity.

How does one address this nonlinearity?

Some authors propose correction stages. Some examples of this can be seen in U.S. Pat. No. 4,743,902 and “A Novel Single-Excitation Capacitive Angular Position Sensor Design”, published in the 2016 Sensors (Basel) journal by Bo Hou et al. In these cases, the authors provide or suggest a correction stage. The error is mapped and a correction is provided. However, this is done by default of observing error and not by the intention of applying or harnessing fringing. Instead, one should embrace fringing, addressing it as effectively as possible.

How does one embrace fringing?

To embrace fringing, one must look at the basic assumptions in commonly used capacitive position sensors. For instance, phase modulation capacitive sensors with three phases can be modeled as follows:

Signal0=A1(x)·Signal1+A2(x)·Signal2+A3(x)·Signal3

Signal 0 is the received signal. Signals 1, 2 and 3 are all emitted signals of different phase. The A1, A2 and A3 components are coefficients that refer to or are based on the capacitive coupling between each emitter and the receiver, through the scale. These coefficients are assumed to change linearly, according to parallel plate modeling, with a change of position or displacement, x. In reality, these equations or transfer functions have nonlinear components, due to fringing, and parasitic capacitive effects.

Sensors with two or more signals emitted or received are really compound amplitude modulation sensors. An example of this is the previous phase modulation capacitive sensor example, with components A1 to A3. Each component varies non-linearly with or against the other components. For phase modulation sensors, the phase of the received signal changes because amplitudes A1 through A3 change. In this case, phase does not vary linearly with position.

What does this mean for enhancing prior art?

Enhancing prior art is done through deterministic understanding and application of the nonlinear fringing principles that govern the capacitive relationships between emitter(s) and receiver(s). In the previous example, the principles can be seen in components A1 to A3. These components can be thought of as elements. To enhance prior art, the fringing behavior needs to be quantified into a form meaningful to the type of data being collected. For instance, the nonlinear and fringing based relationship between phase and position.

f(θ)=X

-   -   where θ is the detected phase         -   X is the displacement along a period.

Such a model can be constructed by analyzing the constituent components and or their fringing principles or behavior. The overall behavior is the combination of the behavior of the constituent elements, the components and or principles. An overall model is built by analyzing, developing and combining the constituent elements and or their behavior(s). Some appropriate methods for analyzing the behavior of constituent elements was discussed previously and includes those found in prior art “Efficient Design of Capacitive Sensors Using Conformal Maps”, published in the 2012 IEEE International Instrumentation and Measurement Technology Conference Proceedings journal by Graz, N. Eidenberger, S. Wiesmueller and B. G. Zagar, pp. 1308-1313. and “An Analytical Fringe Capacitance Model for Interconnects Using Conformal Mapping”, published in the V25, No. 12, December 2006 edition of IEEE Transactions on Computer-Aided Design of Integrated Circuits and System. Other methods also exist.

Such a model can be implemented through a variety of means. These means will be obvious to anyone skilled in the art of capacitive sensing and microelectronics. It is likely that a low-cost microcontroller would be used to implement such a model. However, any reasonable sort of computation unit can be used.

When the nonlinearity is accounted for by known deterministic knowledge, it no longer represents a source of inaccuracy, but improved accuracy.

Embodiment 3 Multiple Groupings

In the first embodiment's amplitude modulation sensor, all of the receiver and or emitter pads are connected in parallel, in one grouping. To enhance sensor performance, the encoder could have more than one grouping. Pad groupings could be like the offset sensing electrodes seen in FIG. 19 (a top view) and FIG. 20 (a side view). Groupings (11A), (12A) are offset from (11B) and (12B). The purpose here can be multi-factorial. For instance, as seen in FIG. 21, the slope of (31) is uniform across an interval. However, this is not realistic. Waveform (32) is more realistic, visualizing how the waveform's slope can change over an interval. The sensor is less accurate in the regions where the slope is less. In this case, the sensor is least accurate in the region of the peaks and valleys. It is simple enough to offset two, or perhaps more, different sets of receivers, or emitters, or receivers and emitters for the purpose of selecting the set that provides the highest degree of resolution at any given point in time or space of the sensor's operation. An example of this can be seen in FIG. 22. Other benefits also exist.

First and foremost: What is a grouping?

A grouping is defined as having one or more pads or segments. If there are two or more segments, they are electrically connected together in parallel. A grouping may be an emitter grouping, consisting of one or more emitter electrodes. A grouping may be a receiver grouping, consisting of one or more receiver electrodes. A grouping may be defined as a combination pair, consisting of emitter and receiver electrode(s). The emitter electrode(s) part of the pair energize or drive that pair's receiver electrode(s).

To drive or energize means to apply signal(s) necessary to perform measurements of or using the capacitive circuitry. Such signal(s) are generally high frequency in nature, from a Signal Generator like component (05). For instance, phase modulation capacitive sensors do not measure capacitance. Rather, they measure phase which is based on the alignment of the capacitive circuitry. However, other methods to evaluate capacitance or take measurements using capacitive circuitry are also possible. For instance, capacitance can be evaluated by applying a constant current and measuring the change in voltage.

A grouping's pad(s) are distinct from the pad(s) of another group. If a group has two or more pads, they are located physically together and not intermixed with the pad(s) of another grouping. Given two groups each with two pads, group A and group B, group A pads are arranged A-A, and group B pads are arranged B-B, where ‘B’ defines one electrode and B-B defines two side by side electrodes. Mixing would be defined as something along the lines of A-B-A-B.

Groupings will have a clear distinction from one another. For starters they must not be mixed. Additional distinction can be manifested through physical spacing, separation, offset and or isolation. This will help reduce inter-group crosstalk, signals from one group contaminating another group. Intra-group crosstalk, contamination between pads in the same group, is not a concern because the pads within a group are connected in parallel to begin with.

It may be desirable to increase the isolation between groups more than is achieved through offset. Achieving isolation can be done through methods of electrical separation and or time slotting. Electrical separation may involve orthogonality or shielding and is discussed in the next section.

For ease of discussion, the focus will be mainly on the restrained case of offset groups of receivers. It is implied that the concepts discussed for this one case can be generalized to other cases.

Discussion on Groupings

FIG. 19 shows emitters and receivers grouped into sets that are physically offset. All (12A) pads are in parallel to form Group A. All (12B) pads are in parallel to form Group B. In this case, Group B is spatially offset from group A by 90 degrees, or half the width of a scale pad. This will result in the repeating waveform from group B's measurements to lead or lag the repeating waveform from group A's measurements by 90 degrees. Half of a period of a waveform is visualized in FIG. 15, by waveform (30). The half not shown is symmetrical to the half that is shown. If desired to increase isolation between groupings, the groupings can be placed a distance apart from one another. Physical space or offset between groupings will help prevent cross-talk. However, it may be more desirable to place shielding pad(s) or shielding electrode(s) between groupings instead. The shielding electrode(s) can be of any appropriate size. It may be desirable to optimize their size, particularly their width. This optimization is to balance bulk (size) to performance in relation to the offset interval desired. Shielding will help reduce and or prevent crosstalk and noise.

There are also other methods to help reduce crosstalk. In particular, for each group with a respective emitter, each emitter and or emitter receiver group pair can be driven or energized with different signal(s) from the Signal Generator, component (05). It may be desirable for some or all signals to be orthogonal to one another. In particular, it may be desirable for signals on adjacent or nearby groupings to be orthogonal in nature. Signals can be orthogonal in time and or frequency.

Examples of shielding between groupings can be seen in FIG. 19, FIG. 20 and FIG. 23. The barrier or shielding is component (13). If desired, each grouping's orthogonal signal can be isolated from one another on the receiving end by the Signal Conditioning Unit, component (06). This isolation separation is particularly true with emitter receiver pairs. The receiving circuitry can be adjusted for each group in such a way as to accept or filter only for the signal associated with that group when taking measurements from that group. A number of separation or filter methods are possible and their implementation should be obvious to anyone already skilled in the art of electronic communications.

Isolation can also be improved by time slotting the sensor's operations. The pads could effectively pass a time window back and forth, where only one or certain groups get to function at any one time. Perhaps only one group functions during this time window. Perhaps only certain groups, likely far apart, function during this time window. Perhaps only one group out of every adjacent set of groups functions during a time window. Regardless of the method of splitting up the time into windows, the idea is to prevent contamination, cross-talk and or noise by systematically setting up what happens when.

When pads or groups are not in use, particularly during time slotting operations, they can function as shielding. This can be achieved by connecting receivers, emitters, etc to ground, or to shielding circuitry in such a way as to make them function as active or passive shielding Some micro-controllers, like Cypress PSOC's, enable pins to be remapped, which would make re-configuring pads into shields very simple. However, mux's or other switching circuitry could be used for this task. A variety of possibilities exist and shielding should be well known to someone skilled in the art of capacitive sensing.

A sensor with simplified groupings is visualized in FIG. 23. In this case, the emitter(s) are condensed into a single large electrode, (11). By condensing the emitters into a single electrode, the encoder is simplified—one source of cross-talk is no longer a concern and orthogonality does not need to be considered. It may be desirable to place a barrier between the emitters and receivers, between different pad groupings and around the outside to reduce other sources of cross-talk and noise. Other shielding configurations are also possible.

A possible circuit implementation of the the arrangement outlined in FIG. 23 can be seen in FIG. 24. The circuit is only mildly more complicated than in EMBODIMENT 1. In this example, (11A) is connected to (11B), suggesting a single large emitter as seen in FIG. 23. At bare minimum, only a single MUX, component (09), is needed to choose between the two pathways. Vout is again the received signal. Vselect is used by the Processing Unit (08) to select the pathway of interest. The circuit can be slightly simplified from this figure, by allowing the two pathways to share access to a single load impedance. The load impedance can be connected after the MUX. Whichever path is connected gets connected to the matching impedance also. Whichever is not connected gets left floating.

A shared impedance can be left static regardless of the source. The impedance can also be adjusted for each source or grouping.

It may be advantageous to use two (or more) Signal Conditioning Units (06), Demodulation Units (07), etc, instead of a MUX (09) directing the signal to one Signal Conditioning Unit, component (06). In that case, the encoder can take multiple measurements simultaneously. Other configurations are also possible, depending on the designs needs of a particular situation. For instance, if more than two groupings are desired, a larger MUX (09) can be used or more Signal Conditioning Units (06), Demodulation Units (07) or other circuitry as appropriate to support the increased number of groupings.

Purpose, Use and Applications of Groupings

The concept of a group has been defined. Some methods of implementing groups have been discussed. Now, it is important to explore how multiple groupings can be used to enhance sensor operation.

1. Irregularity Detection

-   -   Beyond Existing Art     -   Methods of Comparison

2. Irregularity Recognition

-   -   Pattern Matching     -   Pattern Catchall     -   Pattern Learning     -   Pattern Classification

3. Irregularity Adaption 4. Irregularity Avoidance 5. Selection and Data Optimization 1. Irregularity Detection

Multiple groupings would enable a micro processor or processing unit to cross examine measurements. By cross examining measurements, errors, faults and irregularities can be detected.

An early form of error detection from multiple receiver(s) can be seen in U.S. Pat. No. 4,743,902. In that patent, the author proposes taking two measurements, one from one receiver pad, and one from another. If the measurements deviate from one another, the author suggests that an error has occurred; likely from dirt or damage and that the sensor requires cleaning or servicing. This is a simple way of performing error checking. However, this method has some drawbacks and limitations. A problem impacting one pad may also impact the other. For example, dirt could easily smear evenly across both pads as the slider moves around. Both receiver pads may yield the same measurement, even if there is a problem. This would result in a false negative, or undetected error. It would take additional information, such as historical knowledge to evaluate a fault condition in a scenario like this.

To overcome prior art limitations and to enhance error detection, more levels of analysis are needed. The prior art compared the individual measurements between two individual receivers. In this embodiment, not only can the current data be compared, but also historical data. Historical data can be used to help develop velocity and acceleration. The position, velocity and acceleration data for any two or more groups can be compared.

Similarly, the acceleration or velocity data can be used to ensure no points of discontinuity occur. If it seems that the sensor position, velocity or other data has jumped or been otherwise inconsistent, then an error must have occurred. Moreover, the velocity and acceleration data can be used to project what the next measurement(s) should be. Functions like estimators can use historical and present data to approximate the position in the future. This approximation can be tested against the actual measurement or data. Deviations between these quantities will suggest cause for concern.

There are many ways of doing such comparisons and operations. A brief exploration of a few possible comparison operations are detailed as follows:

Basic Comparison of Measurements

1. Gather raw data from each grouping within a reasonable snapshot in time. It may be desirable to perform filtering operations on the data at this point in time.

Raw Data:

-   -   Φ_(A) measurement from grouping A     -   Φ_(B) measurement from grouping B     -   Φ_(C) measurement from grouping C         -   etc

2. Assume

f(Φ)=Position

where f(Φ) represents the nonlinear mapping between a data measurement and position.

3. Evaluate

f(Φ_(A))=X _(A)

f(Φ_(B))=X _(B)

f(Φ_(C))=X _(C)

-   -   etc

where X_(A) is position suggested by the measurement data Φ_(A) from grouping A.

4. Given that groupings are a fixed distance apart, then

f(Φ_(A))=X _(A)

f(Φ_(B))=Δ_(BA) =X _(BA) ={circumflex over (X)} _(A)

f(Φ_(C))−Δ_(CA) =X _(CA) ={circumflex over (X)} _(A)

-   -   etc

where X_(BA) represents {circumflex over (X)}_(A), an estimate of X_(A) based on measurement B and the known distance between groupings A and B, Δ_(BA).

5. No measurement is perfectly without error, so some boundary of acceptable error must exist

(X _(B) −X _(BA))≤Δ

(X _(C) −X _(CA))≤Δ

-   -   etc

for each X_(BA), X_(CA), X_(CB), etc, that exist, Δ represents the boundary of acceptable error. Any deviations outside this boundary of expectation suggest an irregularity has occurred.

Comparison Using Historical Data

1. Given that f(Φ)=X, then

{dot over (f)}(Φ)={dot over (X)}

{umlaut over (f)}(Φ)={umlaut over (X)}

using any reasonable method to compute derivatives. {dot over (X)} is velocity and is {umlaut over (X)} acceleration.

2. Evaluate

{dot over (f)}(Φ_(A))={dot over (X)} _(A)

{dot over (f)}(Φ_(B))={dot over (X)} _(B)

f(Φ_(C))={dot over (X)} _(C)

-   -   etc

No measurement is perfectly without error, so some boundary of acceptable error must exist

({dot over (X)} _(A) −{dot over (X)} _(B))≤Δ

({dot over (X)} _(A) −{dot over (X)} _(C))≤Δ

({dot over (X)} _(B) −{dot over (X)} _(C))≤Δ

etc

where {dot over (X)}_(A) should be equivalent to {dot over (X)}_(B) and {dot over (X)}_(C), etc. Δ represents the boundary of acceptable velocity error. Any deviations outside this boundary of expectation suggest an irregularity has occurred.

3. Evaluate

{umlaut over (f)}(Φ_(A))={umlaut over (X)} _(A)

{umlaut over (f)}(Φ_(B))={umlaut over (X)} _(B)

{umlaut over (f)}(Φ_(C))={umlaut over (X)} _(C)

-   -   etc.         4. No measurement is perfectly without error, so some boundary         of acceptable error must exist

({umlaut over (X)} _(A) −{umlaut over (X)} _(B))≤Δ

({umlaut over (X)} _(A) −{umlaut over (X)} _(C))≤Δ

({umlaut over (X)} _(B) −{umlaut over (X)} _(C))≤Δ

-   -   etc.

where {umlaut over (X)}_(A) should be equivalent to {umlaut over (X)}_(B) and {umlaut over (X)}_(C), etc. Δ represents the boundary of acceptable acceleration error. Any deviations outside this boundary of expectation suggest an irregularity has occurred.

Comparison Using Estimation

1. Evaluate an estimation of the next data using any reasonable method. For instance:

X[k]+{dot over (X)}[k]·ts={circumflex over (X)}[k+1]

-   -   where ts is the time between samples     -   where {circumflex over (X)} is a prediction or estimate     -   where k refers to the k^(th) sample.

This step uses a 1 step, 1^(st) order estimation technique to approximate the next position. It may be desirable to use historical data to estimate current and predict future data. If desired, a higher order estimator or any reasonable prediction method could be used. This estimation step can be done to estimate the position for every grouping.

2. Compare the predicted or estimated position to the measured position when possible

(X[k+1]−{circumflex over (X)}[k+1])≤Δ

No measurement is perfectly without error, so some boundary of acceptable error must exist. This is represented by Δ. The comparison can be performed for every grouping.

Other comparison techniques and methodologies can and do exist. In particular, it may be desirable to estimate using the raw data itself, instead of the position measurement the data points to. However, the key element here is the usage of multiple groupings to perform comparison and cross comparison using past and present data. Any data that violates the boundary of expectation or is inconsistent is suggestive of an error, fault or other irregularity.

When an irregularity is detected, the user or control or feedback system using the position sensor can be informed.

2. Irregularity Recognition (Identification)

Many different types of problems or situations will leave a signature or pattern on the sensor performance in that area. Recent data can be retained and a waveform constructed. This waveform can be analyzed to identify patterns. Any patterns that cannot be identified can be put in their own catchall classification(s) or other categories.

How would pattern matching or signature identification be performed? There are many ways of performing signal identification. One way, for the purpose of proof of concept, is the mathematical correlation or cross-correlation of discrete signals. This type of correlation is commonly used in signal processing and should be well known to anyone skilled in the art of communication systems. The sensor could have many waveform patterns in memory, each corresponding to a known type of irregularity. If an irregularity occurs, such as when an actual measurement deviates from expectation, a comparison can be performed. A waveform segment, partial or whole, of the irregular measurements can be compared against the waveforms of known irregularities. The waveform with the highest correlation to the measurements can be considered the cause of the irregularity. If all correlations lie below some threshold, then the cause may be unknown. New or unknown irregularity waveforms can be added to memory, in a sort of learning feature. Each new or unknown irregularity can be given a new and or arbitrary categorization in memory. Not only can future irregularities be compared to various waveforms with known cause, they can also be compared to various acquired waveforms with unknown cause.

Newly acquired waveforms of unknown cause can be distinguished from one another through a variety of methods. One way would be to establish a correlation threshold. If none of the existing waveforms in memory match the currently encountered irregularity with at least some meaningful degree of correlation, then the irregularity can be given its own new category. For example, unknown waveform #1, unknown waveform #2, etc. Thus, the cause of irregularities encountered in the future can be attributed against these unknown causes, like unknown cause #2.

The waveforms in memory can also be superimposed in various combinations, then correlated against the irregular measurements to evaluate if some combination of expected irregularities have caused the current irregular measurements. Many other methods are also possible.

3. Irregularity Adaptation

When the sensor encounters an irregularity, it effectively encounters a blind spot. It expects and can understand a waveform of a certain shape, like a map. However, the irregularity is causing a waveform of a different shape. The sensor does not know how to interpret the new waveform, it does not have the right map for the situation. The sensor can use multiple groupings to adapt to the new waveform, to make a new map. Using groupings not or less impacted by an irregularity, the sensor can scaffold information and measurements from the regions it can interpret against the regions it can't interpret. In this way, it can generate a new map. With the new map, it can understand and interpret the new waveform. This way, the sensor can see its way through an irregularity. This can be achieved by:

1. Detection of irregularities. 2. While one (or more) groups are impacted by the irregularity, one (or more) groups not or less impacted by the irregularity can be used to gather measurements (ie, position) against which the irregularity's measurement(s) or waveform can be correlated. 3. Maintain a record in memory of the nature of the unique measurement(s) or waveform, as well as the new correlation or mapping caused by the irregularity and where along the scale it occurred. 4. In the future, the sensor can use the newly assigned mapping or correlation for that region of the scale. The sensor can use the new map to sense or help sense position in the areas where that irregularity has occurred.

In summary, the system has made visible what was blind. The sensor can now continue to use the irregular section to sense or obtain measurements.

4. Irregularity Avoidance

The sensor can also perform irregularity avoidance. If the irregularities are very localized, like debris (50) in FIG. 25, the sensor can skip around the irregularity. The sensor doesn't physically skip around the irregularity, but it can skip where its sensing or focus is around the irregularity. For instance in FIG. 25, the debris is under grouping A. While the debris is under grouping A, the sensor can use the data from grouping B to evaluate position. Likewise, as the slider moves along, the debris may find itself under grouping B instead. In this case, the sensor can switch from evaluating position using grouping B's data to using grouping A's data.

The sensor can detect irregularities using the previously discussed irregularity detection. The sensor can also remember or know in advance the locations and possibly other details (such as type, length, etc) about irregularities on the scale. Using detection and or advanced knowledge, the sensor can actively and intelligently select groupings away from, least impacted or not impacted at all by the problem or irregularity. To select groupings implies using the data from those groupings to evaluate quantities like position. When the sensor selects data not or least impacted by an irregularity, it selects for the best or most trustworthy data. In this way, the sensor avoids irregularities at any given point or interval in time and or space of the sensor's operation. Other methods of avoidance are also possible.

Regardless of the method of avoidance, the idea here is to change which data or data source(s) are being used to help construct desirable information. In particular, to exclude the use of data from bad sources and include the use of data from good sources at any given point in time and or space of the sensor's operation.

5. Selection and Data Optimization

The concept of choice requires a method of evaluating options. Evaluation requires a definition of best, a prioritization of goals and a balance therein. For position sensing, it is important to maximize exactness of a measurement. The best measurement is the most exact measurement.

However, it is also true that a measurement can be faulty or in error. Thus the best measurement can also be seen as the most reliable or trustworthy measurement.

How to maximize exactness?

The result of having two pathways to choose between can be seen in FIG. 22. The steeper the slope, the greater the signal distinction between any two measurements. The greater the signal distinction, the more accurate the information. If a sensor has two (or more) sensor pad groupings to choose from, it can decide to measure any particular grouping and take regular measurements from every group. By taking the derivative between any two or more measurements from the same group, the sensor can evaluate slope for each grouping or source. By comparing slope, the sensor can evaluate the source, or perhaps source(s), with the greatest distinction at any point or interval in time and or space. Based on this approach, the best data is the data with the greatest distinction. Thus, the best source upon which to base a measurement is the source experiencing the greatest or steepest magnitude of slope at any point or interval in time and or space. A variety of other comparison or evaluation methods are also possible.

An example of a sensor selecting the group with the steepest slope can be seen as follows. The measurements from two offset groupings are visualized in FIG. 22. Plot (A) represents the complete waveforms from both groupings, grouping A (33A) and grouping B (33B). Plot (B) represents the measurements with switching action at the location of the vertical lines. Plot (C) represents the overall resulting waveform, when only the regions of interest are selected. R1, R2, R3 and R4 represent individual components of the waveforms from (33A) and (33B) that are used to make an overall resulting waveform. These components represent the regions or segments of steepest slope of (33A) and (33B). The overall waveform as seen in plot (C) allows for more accurate position information than either waveform by itself, a synergy. It is also possible to perform analogous operation with more than two groupings or sources of waveforms.

How to maximize reliability?

The best data should always be the data not impacted by any sort of irregularity or error. However during sensor operation, situations may occur where no such data exists. Therefore, the next best data should be the data that can be derived from grouping(s) experiencing an irregularity that has already been adapted to. If no such situation exists, then the best data is the data from a group or groups that are experiencing the least deviation from expectation.

In some situations it may be desirable to arbitrarily define what data or data characteristics constitute best. This can be determined by different programs that define sensor behavior, or by user input.

In some situations, it may be desirable to know in advance where the best data exists. To do this, it is important that the sensor behavior is mapped or known completely in advance. Perhaps during a startup learning stage or perhaps even programmed from the factory. By knowing the behavior in advance, the regions with the most trustworthy and or most exact (steepest slope) can be isolated.

According to predetermined behavior or parameters, the sensor can switch which source(s) it uses to evaluated the desired quantities (ie, position). For example, perhaps when the readings from one grouping fall in a certain range, that source becomes the data source. When the readings fall outside of a target range, another group that is inside the target range becomes the data source. The main idea here is minimal or minimizing the processing required.

Embodiment 4 Pad Specialization

This embodiment extends or builds on the concepts in the previous embodiment, Multiple Groupings. In the previous embodiment, additional pad groupings were used to enable measurement optimization, irregularity detection, adaptation and avoidance, as well as for other tasks. In that embodiment, pad groupings were reused, from one task to another. In this embodiment, it is proposed to break down tasks. To have specialized pads for particular purposes or goals, instead of, on top of or as well as the previously discussed pad grouping(s). This could be achieved through many mechanisms, such as but not limited to: unique pad sizing, shape, spacing, placement, connection, interconnection, configuration, reconfiguration, driving signal(s), etc.

Specialized pads will operate or collect capacitive measurements much like other pads or groups. The nature of their measurements will be in accordance with their niche. For instance, they may be used to detect misalignment information. To make sense of niche information, specialized models that correlate the data to the quantity being measured can be used. For example, a specialized pad used to measure gap distance may feed a model that utilizes the inverse relationship between gap distance and capacitance. Such a model enables the evaluation or reasonable approximation of gap distance. Other models would be useful for other situations.

What are some illustrative examples of specialized pads? FIG. 25, FIG. 26 and FIG. 27 are examples of specialized pads. In FIG. 25 and FIG. 26, pads and pad pairs are placed on either side of the normal position sensing group(s), pads denoted by (14), (14A) and (14B), (14C) and (14D), respectively. In these examples, the pads are special because of their position. Being located on either side of the slider, they can perform prescanning Irregularities and general scale terrain characteristics or conditions can be detected or evaluated. The irregularities can be detected before they come into vicinity of other specialized pads, non-specialized pads and groups; detecting a problem in advance of it manifesting itself. The degree of the problem can be evaluated using models specialized for irregularity identification, similar to that outlined in the previous embodiment. For instance, the physical length of an irregularity can be estimated using data from the prescanning pads. Using this information, the sensor can devise its response: to inform, to avoid, to adapt or some other desired action as per embodiment 3. Even the imprecise detection of irregularities will enable the sensor to engage in anticipatory actions or alert, avoidance or adaption, or some other behavior as desired.

In FIG. 25 and FIG. 26, the same prescanning pads are used to provide all irregularity detection. It may not be reasonable to re-use the same prescanning pads to detect multiple or all irregularities or fault conditions. It may be beneficial to have more than one specialized pad(s), each for different tasks or purpose.

In FIG. 27, pads are both specially placed and shaped. When compared to FIG. 26, pad (14A) through (14D) are split into (14A-1) and (14A-2), (14B-1) and (14B-2), (14C-1) and (14C-2), (14D-1) and (14D-2). These split pads allow for the normal prescanning and irregularity detection, as well as a more perceptive detection of misalignment. When in comparison to the split pads proposed in prior art US patent US 2015/0268790 A1, this embodiment's split pad manifestation is simpler. Only the specialized pads are split to detect misalignment, instead of all of the pads. When only certain pads are split, non-split pads and groups can be used to provide more accurate position measurements.

Imbalances of capacitance between pads, like (14A-1) and (14A-2) suggest misalignment. A variety of analysis techniques are possible if the connections to and with these split parts, (14A-1) to (14D-2), can be modified. This is possible with switch and or MUX components. These components can be discrete or built into existing microcontrollers, like the Cypress PSOC 4 chip series. Other components may also perform the necessary, on the go, routing changes. Split pads like (14A-1) and (14A-2) can be in parallel, as emitters in one moment. They can be in parallel as receivers in another. They can be in series as receivers, where a measurement for (14A-1) is taken independently of (14A-2). Measuring these pads separately makes the detection of imbalances and hence misalignment easier. Other routing approaches are also possible.

Using switches or MUXes, it is possible to change the specialized pad connections. The specialized pads can be switched from the scanning electronics to the shielding electronics. This provides the specialized pads more function, allowing them to act or operate as shields. These specialized pad functions can be time sliced with one another and or other sensor functions. For example, the sensor can take position measurements and prescanning measurements at different time intervals. During a position measurement, specialized pads could provide shielding. This specializes how the pads can function and configure. This eliminates or reduces the need for separate shielding electrodes.

It may also be desirable to isolate the function of specialized pad(s) from one another or from other parts of the sensor by driving them with signals orthogonal in time and or frequency to the signals used nearby, elsewhere and or in the rest of the circuit.

Embodiment 5 Absolute Positioning

Many capacitive sensors do not have true absolute positioning. For instance, many keep track of the number of intervals traversed, a sort of coarse information.

Some capacitive sensors attempt to embed absolute information into the scale. Some of these methods include having two rows, one for relative and one for absolute information, like in U.S. Pat. Nos. 6,892,590 B1 and 4,879,508. Another method involves a single row with the occasional, and intentional missing pad, like in US patent US 2015/0268790 A1. These allow the sensor to evaluate position absolutely along the scale without manual indexing

This embodiment means to provide absolute position information, embedded in the scale. This embodiment is possible based on two concepts:

1. Irregularity detection as outline in previous embodiments. 2. The innate and developed understanding, application and optimization of fringing.

Linear and fringing capacitance, as applied to absolute positioning, implies unique features—like land markers—to designate or divide regions uniquely. There are a number of ways to imbue the scale with unique features.

Features:

1. Unique pad shape and size 2. Connection Swap (crossover)

3. Unique Spacing

Any one or more of these features can be embedded into the scale and used as an index or marker for absolute positioning or referencing.

1. Uniquely Shaped Pads, Sizing and Overlap

Prior art, U.S. Pat. No. 6,483,321 B2, proposes changing the rotor radius in a radial capacitive sensor to denote absolute position. However, there are other unique features that can also be embedded in the scale to denote absolute position or act as embedded features. Conformal mapping shows that capacitive behavior is based on the size and shape of the pads involved. Using this knowledge, it is a natural extension that uniquely shaped pads will exhibit unique capacitive behavior.

With the irregularity identification outlined in prior embodiments, pads of unique shape can be identified. A pad with an indent can be uniquely identified. A pad with a spur or outward extrusion can be uniquely identified. Pads that are wider can be uniquely identified. A pad that is thicker, perhaps there is a bit of solder on its surface (intentionally), can be identified. All these unique pad features can be identified because of their unique capacitive behaviors.

Likewise, the prior art details varying pad length in a radial sensor. Only a single rotor blade pad or segment needs to be varied in a radial sensor. Due to the circular nature, it will always function to denote absolute position. However, on a mechanically linear sensor it may be desirable to vary more than one blade along the length of the scale to effectively denote absolute position markers along its length. Therefore, it is useful to extend the prior art concept to mechanically linear capacitive sensors.

A visualization example of unique pad shape can be seen in FIG. 28. In this figure, the additional features are seen as over-sized pads, as denoted by components (21-1A) and (23-1A). The center of the over-sized pads is labeled (20-1), corresponding with the center of the waveform in FIG. 29.

As the slider, in FIG. 28, moves towards the right (in the positive X direction), the unique features will overlap with the grouping formed by (11B) and (12B). As the unique feature overlap increases, an additional capacitive behavior will be superimposed. This is visualized in FIG. 29, where the pseudo-sinusoid (34) is higher towards the center. The center peak represents where the feature (20-1) is underneath one of the slider's groupings, with 100% overlap. This upwards motion is the result of linear and fringing capacitive behavior. In FIG. 28, one feature was added. However, any number of features is possible.

By way of innate fringing knowledge, the impact of a pad shape and or size feature can be known in-advance, allowing for identification. Since these features are intentional and can be identified, they are intentional irregularities, and can be used as a way of encoding higher order information into the scale.

2. Connection Swap (Crossover)

The scale pads are comprised mainly of three parts, as illustrated in FIG. 30. Component (21) couples capacitively with emitter(s). Component (23) couples capacitively with the receiver(s). Component (22) conductively connects (21) and (23) together.

Component (22) may be a simple copper trace on a PCB. Other manifestations are also possible. It may be on plane, as (22). It may be tucked away to the other side of the PCB, as (22-P1). It can also be tucked away like (22-P2), routing to a pad on another layer. Such a pad is denoted by (23-P2). Other routing is also possible.

A conductive connection lends itself to being modified, perhaps for the unique features previously mentioned. This modifications could be any variety of possibilities. A simple modification would be to swap or crossover the conductive connection, like in FIG. 31. In this figure, the deviation of (22-C1) and (22-C2) from how (22) is otherwise routed represents an example of crossover.

Why would crossover or cross connection be useful?

This cross connection could allow for unique signatures. A simple variation of this signature would detect the crossed pads as they enter the scanning or prescanning region. At this point, one of the crossed pads will lie outside of the scanning region. This will interrupt the normal connection between emitter and receiver. The capacitance will be measurably impacted when this happens. Many other variations are possible.

Different connections, such as having three pads crossed, can encode more information. The way in which cross connection(s) are done can encode binary information. For example, a straight and normal connection, like (22) as depicted in FIG. 31, could be a zero. A crossed connection, like (22-C1) and (22-C2) in FIG. 31, could be a one. In this sense, very distinct digital information can be embedded and then read, analogous to braille. It could encode a binary pattern for absolute positioning. Instead of connection swaps, other irregularities can also be used in an analogous way.

The cross connection could be used across layers. One way of doing this is clear in the comparison of FIG. 32 and FIG. 33. FIG. 32 has no cross connection. It shows grouping A, components (11A) and (12A), capacitively coupling with scale pads, (21A) and (23A), respectively. It also shows grouping B, components (11B) and (12B), capacitively coupling with scale pads (21B) and (23B), respectively. FIG. 33 has a cross connection. (11A) and (21A) are coupled, as are (12B) and (23B). The coupled pairs are connected together, (11A) to (12B) due to crossover (22B-C). Similarly, (11B) and (21B) are coupled, as are (12A) and (23A). The coupled pairs are connected together, (11B) to (12A) due to crossover (22A-C). The emitter on one side has one signal. The emitter on the other side has another signal. The cross connection between layers is an identifiable irregularity. The system detects which side's signal it is receiving on each side, identifying the crossover irregularity.

This coupling between layers can occur for one, some or all of the pads in the scale. The coupling does not have to connect two adjacent pads, nor does it have to be the cross connection of two pads or pad groupings. Many different methods are possible. PCB traces and vias make this easy.

In prior art, US patent US 2015/0268790 A1, the author proposes an embedded feature for absolute positioning: missing pad(s) in the scale. It is possible to imbue an analogous feature but through a simpler alteration: removal of part of a scale pad or segment, scale component (22). This component can be removed for individual scale segments, elements or in localized areas of the scale. In this way, the normal crosstalk behavior between adjacent scale pads will be more readily preserved when compared to extracting an entire scale pad or segment. Even though crosstalk is generally undesirable, it is still part of the normal behavior of the scale segments or pads. The complete removal of a pad would upset this crosstalk and hence upset the accuracy of the models that describes the Capacitive Circuitry behavior. The behavior of the scale in the region surrounding the irregularity is more readily preserved when fewer alterations to the scale are made. Therefore, removing an individual (22) component for any individual segment on the scale will help retain normal sensor performance in the regions surrounding the intentional alteration or irregularity. The removal of (22) could represent a “no connection” case.

It may be desirable to offset the pads in the top (10A) and bottom (10B) of components in FIG. 33 analogous to how groupings (11A) and (11B) are offset in FIG. 20. This is to reduce unintentional cross capacitance or contamination between layers. Instead of offsetting pad groupings on the same plane, each plane is offset relative to one another by one half of an interval in the X-direction. This would make it easier to treat each side as its own pad grouping, like in embodiment 3.

There are variety of other methods to prevent layers from interfering unintentionally with one another. One way is to make (20) in FIG. 33 thick enough that the unintentional cross-capacitance between the top and bottom is negligible; capacitance is generally the inverse of gap distance. Other methods are also possible. To prevent interference, it may also be desirable if the signals on each side are orthogonal to each other, such as in time or frequency. To prevent interference, signals and layer operations can also be time slotted.

The act of cross connection is like flipping, activating or triggering a switch. If the layers are offset, then even with the same emitted signal on both sides, the cross-connection will be an identifiable irregularity. If each layer is driven with a different frequency, phase or other characteristic, then the cross-connection will be an identifiable irregularity, even if the layers are not offset. The identifiable features will be noticed on an irregularity identification search. They do not even have to be explicitly recognized or categorized, just noticed. The pattern of things noticed can be corresponded to information. For analogous example, with braille, one may feel a pattern of bumps. The height of those bump may be indeterminate or imprecisely determined. However, the presence of that pattern is detectable.

These cross-connections and related patterns can be detected and identified. Through identification, they become intentional feature(s) or irregularities. Such intentional irregularities can be used to encode higher order information into the scale. This higher order information can be used to communicate information such as absolute position.

3. Unique Spacing

Pads of varying size, shape, and cross connection were explored, but of uniform and repeating position. Every scale pad is positioned equidistant to each next pad. However, it is fully possible to imbue position information by spacing, placing and or distributing the scale pads in different ways. Different pad realizations will yield different capacitive distributions. These capacitive distributions can be ‘read’ and reverse analyzed to determine absolute position.

Chicken eyes have cones spaced very uniquely. Human eyes have a more regular and periodic cone spacing, with a higher clustering towards the center of the eye. However, chickens do not have such a regular cone spacing. Cones are grouped in periods. Within a period, the cones are spaced in random patterns. These patterns obey certain boundary rules. The cones are not too close together, nor too far apart.

The cone layout can be characterized by the following points: regular and dependable rules and boundaries, irregular and or unique spacing, and regular intervals.

Why are these points worth interest?

Random, patterned or unique spacing provides information. Specifically, it provides position information. As the chicken looks at an object, the object enters different regions of unique spacing. The unique spacing codes the visual information with spatial meaning. As the chicken moves its head, it can track an object, without moving its eyes in their sockets. The cone intervals, periods, are like clusters. The spatial position of the object is reflected by which clusters it lies inside of.

This kind of cone layout requires less processing. Chicken brains are very small. Human brains are much larger. This method of spatially coding information at the sensor level enables chickens to have a high level of spatial awareness without as much gray matter. The overhead is reduced.

Micro-controllers, when compared to computers, are similar to how a chicken brain is to a human brain. In order to achieve higher orders of performance, creative methods are needed. The pad spacing on a scale can be arranged using the principles of the chicken eyes. Any one or more individual pads can be spaced differently along the length of the scale. Pads of various size, shape and crossover can be distributed, placed and or spaced differently along the length of the scale. Provided the spacing, placement and or distribution enables unique capacitive behavior, then their uniqueness can provide absolute and relative positioning information. For example: Too close together, and there isn't discernment. Too far apart and the fringing isn't strong enough to be meaningful. The goal is to strike the right balance of how features are distributed to optimize the resulting capacitive waveform.

The unique pad spacing can be detected and identified. Through identification, unique spacing(s) become intentional feature(s) or irregularities. Such intentional irregularities can be used to encode higher order information into the scale. This higher order information can be used to communicate information such as absolute position.

In summary of the intentional features or irregularities discussed in Unique pad shape and size, Connection Swap (crossover) and Unique Spacing, any one or more of these unique features can be detected and or identified with the irregularity detection and recognition discussed in previous embodiments. The presence of any one or more features imbues the scale with higher order information. Details such as but not limited to the nature, presence and or type of irregularity can encode information. This higher order information can be used to communicate information such as but not limited to absolute position. In short, any one or more of the discussed intentional features can be used to provide referencing, indexing or marking for absolute positioning.

Asymmetric Features and Feature Groups

Unique and intentional features can be asymmetric in nature. The placement, distribution and order of these features can also be asymmetric in nature. Asymmetric features and feature distribution can be used to encode higher levels of information such as absolute position but in particular, direction information.

Approaching an asymmetric feature from one side may imply that the slider is traveling in the positive direction, or vice versa. For example, a scale pad could be trapezoidal in nature, as seen by components (21-1B) and (23-1B) in FIG. 34. Being trapezoidal, with a triangular shape on one side, the signal waveform will be uniquely more linear in that region.

Approaching an asymmetric distribution or order of features from one side may imply that the slider is traveling in the positive direction, or vice verse. For example, given two features, A and B, detecting A first, then B may suggest travel in the positive direction. Detecting B first, then A, may suggest travel in the negative direction. In this way, the asymmetric nature of a pattern, or how patterns can be arranged to be asymmetric imbues direction information.

Imprecise Data

The exact nature or type or degree of an irregularity may be unclear. However, that an irregularity has occurred is more clear. Likewise, that a specific pattern of irregularities has occurred is also clear or easier to discern than the details, nature, type and or degree of each irregularity in the pattern. Without necessarily identifying specific details about the irregularity or pattern of two or more irregularities, higher order information encoded in the scale can be detected based simply on the presence of an irregularity or pattern of irregularities. This constitutes a method of imprecise data—using a limited set of characteristics to evaluate higher order information.

In particular, a hysteresis approach can be used, like Yes/No irregularity. This can be seen as a means of detecting binary information encoded into the scale. For example, if an intentional irregularity is one interval long, then a pattern three intervals long could be irregularity, no irregularity, irregularity, or one-zero-one.

Embodiment 6 Embedded Components

Embedded Components:

discrete components embedded in the scale, like resistors, capacitors, etc.

So far, scales for wireless sensors are entirely inert. Their behavior is entirely based on the shape, orientation, etc of the pads. However, scales in wireless sensors could have embedded components on/in them. These components could be resistors, capacitors, inductors, etc. In short, embedded components refers to discrete components. For instance, an additional resistive, capacitive or inductive load can be embedded in the scale. This is illustrated in FIG. 35, where component (42), an inductor, is placed between (21) and (23). The related circuit is summarized on the right hand of FIG. 35. The addition of discrete components can be used to change the electrical characteristics on the output, as another form of intentional irregularity. Even the addition of a load will alter the signal amplitude or capacitive circuitry impedance characteristics. A discrete capacitor could be added at the location of (42), increasing the localized capacitance, being very detectable in nature. The discrete components can vary from one scale pad set to the next, providing variance in electrical characteristics along the length of the scale in the X axis direction. The choice of component(s) and the specification of those component(s) can vary from one set or pad to another, side by side. A set can be defined as components (21), (22-PD), (42), (22-PD) and (23), making up one segment of the scale as visualized in figure FIG. 35. Many configurations are possible. At very high frequencies it may be desirable to embed microwave circuits instead of or as well as discrete components.

The use or purpose of such intentional irregularities is the same as discussed in the previous embodiment. In short, the application of these features into or onto the sensor scale provides a means of imbuing or encoding the scale with higher order information. The higher order information can be interpreted for absolute positioning, evaluating direction, and other purposes.

Embodiment 7 Oversized Pads

Previous embodiments have discussed different unique features for the purpose of absolute positioning Some of the previously discussed features involve pads of unique size, shape or position. One example, seen in FIG. 28, involved having some scale pads that were oversized to be wider than normal, denoted by (21-1A) and (23-1A).

A simple extension or off-shoot from over-sizing and pad shaping for absolute positioning is to oversize and shape the pads to help resist misalignment errors. Particularly translational and rotational errors. The physical reality of the misalignment is not changed, the pads will still be physically misaligned. However, the impact of misalignment on capacitance is resisted—the overlap is maintained and the field lines still have paths. An example of oversizing the slider pads is visualized in FIG. 36. In this example, the slider pads (11C) and (12C) are lengthened in the Y direction. However, it is also possible to widen the pads, and adjust pad shape in other ways to resist errors. One example of this is in FIG. 37, where an oversized batwing shape, in components (11D) and (12D), could help resist rotational and translational errors. It may be desirable to adjust either the scale or slider pads, but not both, in a given design; however it is up to the designer to choose the best pad oversize and shape combination in any particular application. Balancing pad oversizing, as well as pad shape, may be desirable.

Other shapes are also possible.

CONCLUSION

It will be apparent to one skilled in the art that modifications may be made to the illustrated embodiments without departing from the spirit and scope of the invention as hereinafter defined in the claims. 

The embodiments of the invention in which an exclusive property or privileged is claimed are defined as follows:
 1. An improved wireless capacitive type displacement sensing device with segmented scale being comprised of a capacitive circuitry module, a measurement module and an interpreting module with the means for interpreting the property being measured with one or more models that account for fringing.
 2. A method for improving capacitive sensor performance using any suitable means for enabling adjustable load impedance wherein the input impedance of the receiving circuitry can be changed at any time, particularly during sensor operation.
 3. The method described in claim (2.), to adjust the load impedance in such a way as to ensure the received waveform is within a desired range such as but not limited to the receiving circuitry's optimal sensing range.
 4. A method to improve capacitive type displacement sensing where one or more historical measurements are retained in memory wherein: a. historical measurements are used to mathematically project or estimate the next measurement(s) b. actual measurements should be within a boundary or window of expectation of the estimated or projected measurement c. measurements that deviate outside of a boundary of expectation indicate inconsistencies or faults.
 5. The method described in (4.), to use present and or historical measurements in such a way as to determine consistency between measurement(s) and detect discontinuities.
 6. Based on the methods described in claim (1.), a method for modeling capacitive behavior by parts involving: a. mathematically breaking down the resultant signal or signals into their associated capacitance dependent elements b. build deterministic nonlinear and fringe based map or model that correlate data to position, based on the constituent elements c. implement the model using any appropriate method such as a computation unit whereby the sensor's position detection is improved by the implementation and application of deterministic fringing and nonlinear capacitance behavior models.
 7. A more accurate and capable displacement sensor by providing the sensing apparatus choice between two or more sources or ways or methods of obtaining data, where: a. individual slider sensor pads, one or more define a group, where if there are two or more pads, they are connected together electrically in parallel b. different groups are spaced and or placed and or formed differently from one another c. groups are not spatially intermixed with one another, the pad(s) comprising one group are separate from the pad(s) comprising another group d. the difference between groups provides different vantage points or sources from which to obtain data and or measurements e. different vantage points provide the same and or different types and or quality of data at any given point across the sensor's displacement and or in time f. using any device for enabling the sensing apparatus to obtain or collect measurements from any of the groups g. using any device for enabling the sensing apparatus to obtain data, one or more measurements from at least one or more source at a time whereby providing the sensing apparatus the ability of choice enables the optimization of and between data quality, quantity and type.
 8. The method as defined in claim (7.), improved fault or irregularity resilience consisting of one or more of the following methods: a. a method of irregularity detection, where the data and or the quantities suggested by the data from each grouping can be compared for consistency with one another and or with retained historical values and or with estimated data wherein deviation(s) violating consistency, continuity and or expectation suggest irregularity condition situation(s) b. a method of irregularity recognition, where sample or example models or waveforms representing the impact or pattern that different irregularities cause on the base waveform are stored in memory, where in the event of a detected irregularity, the retained irregular measurements or waveform is compared and or pattern matched using any appropriate means, such as but not limited to mathematical correlation, against the stored or known samples c. a method of irregularity recognition, where any pattern that fails to be matched is lumped into a separate catchall classification category in memory d. a method of irregularity adaptation wherein: I. irregularities are detected II. creating or updating the correlation associated with that region of the scale using measurements from other group(s) to establish the quantities, such as position, that are correlated with the capacitance or signal characteristics measured from or by the group(s) impacted by the irregularity III. maintaining a record in memory of the irregularity's unique measurement(s) or waveform to the position mapping and details of where along the scale where it occurred whereby the sensor can apply the new map to the irregular data to evaluate relevant quantities like position in that region of the scale in the future e. a method of irregularity acquisition, where said mapping of a waveform that cannot or is not identified is provided a unique classification and stored in memory as a sample where it can then be used in the future as a sample against which patterns can be compared for identification f. a method of irregularity avoidance where: I. a sensor has two or more groupings or sources from which information can be collected II. the sensor avoids irregularities by not acquiring and or using data or certain types of data to calculate quantities like position from any one or more groupings that are in the vicinity to be and or are being impacted by an irregularity wherein the data used to calculate the desirable quantities, such as but not limited to position, is only taken or based off of the best or most trustworthy data from one or more sources away from, not and or least impacted by any given irregularity at any given point in time and or space.
 9. The method described in claim (7.), data optimization methods vary in accordance with the definition of best, where any one or more of the following methods can be used to define best: a. best according to exactness is evaluated by a process of comparison, any two data sources can be compared, where the greater the difference between a source's measurements, in other words slope, the more distinct or clear its measurements are, where using any reasonable means to evaluate slope between successive measurements for each group, the best data is the data from the source with the most distinct measurements at any point or interval in time and or space of the sensor's operation b. best according to reliability, using any reasonable means for irregularity detection, the best data in any given situation is from the following source(s) in order of quality: I. source(s) not impacted by any sort of irregularity or error II. source(s) impacted by an irregularity, but the irregularity has been adapted to III. source(s) impacted by an irregularity that has not been adapted to, the source(s) with the least deviation from expectation c. best is arbitrarily defined in any way deemed desirable to the user d. best is evaluated in advance, where the behavior across the operating range of the sensor is known in advance and the regions of greatest distinction and or reliability for each grouping are predetermined.
 10. The structure of two or more distinct groupings in claim (7.), enhancing operation by any one or more of the following methods: a. increasing isolation between groupings by means of physical offset or separation between said groupings b. increase isolation between groupings by means of the placement of shield pad(s) between said groupings c. increase isolation between groupings by means of driving one or more groupings with orthogonal signals d. increase isolation between groupings by means of time slotting or interweaving their function or operation with one another e. increase the isolation between groupings by means of changing how pads, electrodes, receivers and or emitter components are connected wherein these components can be connected in such a way as to function as shields or barriers when not in use or as appropriately desired.
 11. A modification to capacitive type position sensors to improve sensor functionality by the process of specialized slider pads, where: a. pad specialization as defined by any reasonable means of making, designing, placing and or operating one or more particular sensor pad(s) or pad grouping(s) to collect particular types of information in which some pad(s) or pad grouping(s) are specialized entirely or partially for detecting features such as but not limited to irregularities while other pad(s) or pad grouping(s) are devoted entirely or partially for detecting features such as but not limited to position b. specialized models, where any reasonable model is used to correlate or derive the information from the quantity being measured or data being collected by any one or more specialized pads.
 12. The improvement described in claim (11.), particular and specialized pad(s) or pad grouping(s) are located on one or both ends of the slider in such a way that they encounter, detect and or sense scale conditions, irregularities, misalignment and or terrain features in advance of being encountered by other pad(s) or grouping(s).
 13. The structure of two or more distinct pad(s) and or grouping(s) as described in claim (11.), enhancing operation by any one or more of the following methods: a. increasing isolation between pads and or groupings by means of physical offset or separation between said pads and or groupings b. increase isolation between pads and or groupings by means of shield pad(s) between said pads and or groupings c. increase isolation between pads and or groupings by means of driving different pad(s) or grouping(s) with signal(s) that are orthogonal in nature d. increase isolation between pads and or groupings by means of time slotting their function or operation with one another e. increase the isolation between pads and or groupings by any reasonable means of connecting either and or both the emitter and receiver components to ground or shielding circuitry in such a way as to make pad(s) and or grouping(s) operate as shields or barriers when not otherwise in use.
 14. The method described in claim (11.), the specialization of pads and or grouping(s) by way of any reasonable means of switching or connection reconfiguration, where the connections between different pads and or groupings, between pads and or groupings and digitization circuitry, between pads and or groupings and signal generation circuitry, between pads and or groupings and shielding circuitry or any other reasonable interconnections in such a way as to enable the active change of the operation and or function of any one or more pad(s) and or grouping(s).
 15. A modification to capacitive type position sensor scale, by the application of intentional irregularities or features by way of any one or more of the following: a. intentional irregularity by way of modifying the width of one or more scale pads b. intentional irregularity by way of modifying the shape of one or more scale pads c. intentional irregularity by way of modifying the thickness of one or more scale pads d. intentional irregularity by way of modifying the length of one or more scale pads on a mechanically linear sensor e. intentional irregularity by way of pad interconnection or crossover f. intentional irregularity by way of no-connection case of pad crossover g. intentional irregularity by the embedding of components in or on the scale, whether those are discrete components, microwave circuit components or otherwise h. intentional irregularity by the modification of the spacing aspects of one or more scale pads i. intentional irregularity by the modification of the placement aspects of one or more scale pads.
 16. The methods described in claim (15.), intentional irregularities placed in such a way as to encode more and or higher levels of information in the scale where: the type, order, placement and or distribution of intentional irregularities encodes information on top of, instead of or as well as position information to achieve one or more of the following: a. intentional features are the means for a sensor to reference or index against for absolute positioning b. intentional features that are asymmetric in nature, order, distribution and or placement are the means for directional indication or encoding directional information where any reasonable method can be used to detect and or identify the intentional irregularities as they are encountered.
 17. The features described in claim (16.), a method of detecting higher order information by way of imprecise data, where merely the detection of the presence of an irregularity or pattern of two or more irregularities is used to detect encoded higher order information such as but not limited to absolute position or directional information.
 18. A modification to capacitive type position sensors, oversizing and or shaping of the slider and or scale pad(s) in such a way as to improve resistance or tolerance to translational and or rotational misalignment errors. 